Integer part problem. [closed]

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Find all positive integers which $fracn+2017[sqrtn+1]$ and $fracn+2018[sqrtn]$ are natural numbers.







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closed as off-topic by Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur Jul 30 at 12:40


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur
If this question can be reworded to fit the rules in the help center, please edit the question.












  • That means that the numerator should be multiple of denominator...
    – MysteryGuy
    Jul 30 at 12:26










  • You use the tag contest-math. What contest is it, and is it over?
    – Arthur
    Jul 30 at 12:29










  • this problem was at romanian math olympiad - the local stage subject
    – mathematiciangrade8
    Jul 30 at 12:35










  • Do you use $[x]$ as the floor function or the nearest integer?
    – kvantour
    Jul 30 at 12:40










  • nearest integer
    – mathematiciangrade8
    Jul 30 at 12:40














up vote
0
down vote

favorite
1












Find all positive integers which $fracn+2017[sqrtn+1]$ and $fracn+2018[sqrtn]$ are natural numbers.







share|cite|improve this question













closed as off-topic by Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur Jul 30 at 12:40


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur
If this question can be reworded to fit the rules in the help center, please edit the question.












  • That means that the numerator should be multiple of denominator...
    – MysteryGuy
    Jul 30 at 12:26










  • You use the tag contest-math. What contest is it, and is it over?
    – Arthur
    Jul 30 at 12:29










  • this problem was at romanian math olympiad - the local stage subject
    – mathematiciangrade8
    Jul 30 at 12:35










  • Do you use $[x]$ as the floor function or the nearest integer?
    – kvantour
    Jul 30 at 12:40










  • nearest integer
    – mathematiciangrade8
    Jul 30 at 12:40












up vote
0
down vote

favorite
1









up vote
0
down vote

favorite
1






1





Find all positive integers which $fracn+2017[sqrtn+1]$ and $fracn+2018[sqrtn]$ are natural numbers.







share|cite|improve this question













Find all positive integers which $fracn+2017[sqrtn+1]$ and $fracn+2018[sqrtn]$ are natural numbers.









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Jul 30 at 12:37









greedoid

26.1k93473




26.1k93473









asked Jul 30 at 12:10









mathematiciangrade8

313




313




closed as off-topic by Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur Jul 30 at 12:40


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur
If this question can be reworded to fit the rules in the help center, please edit the question.




closed as off-topic by Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur Jul 30 at 12:40


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – Clarinetist, Michael Hoppe, 5xum, choco_addicted, Arthur
If this question can be reworded to fit the rules in the help center, please edit the question.











  • That means that the numerator should be multiple of denominator...
    – MysteryGuy
    Jul 30 at 12:26










  • You use the tag contest-math. What contest is it, and is it over?
    – Arthur
    Jul 30 at 12:29










  • this problem was at romanian math olympiad - the local stage subject
    – mathematiciangrade8
    Jul 30 at 12:35










  • Do you use $[x]$ as the floor function or the nearest integer?
    – kvantour
    Jul 30 at 12:40










  • nearest integer
    – mathematiciangrade8
    Jul 30 at 12:40
















  • That means that the numerator should be multiple of denominator...
    – MysteryGuy
    Jul 30 at 12:26










  • You use the tag contest-math. What contest is it, and is it over?
    – Arthur
    Jul 30 at 12:29










  • this problem was at romanian math olympiad - the local stage subject
    – mathematiciangrade8
    Jul 30 at 12:35










  • Do you use $[x]$ as the floor function or the nearest integer?
    – kvantour
    Jul 30 at 12:40










  • nearest integer
    – mathematiciangrade8
    Jul 30 at 12:40















That means that the numerator should be multiple of denominator...
– MysteryGuy
Jul 30 at 12:26




That means that the numerator should be multiple of denominator...
– MysteryGuy
Jul 30 at 12:26












You use the tag contest-math. What contest is it, and is it over?
– Arthur
Jul 30 at 12:29




You use the tag contest-math. What contest is it, and is it over?
– Arthur
Jul 30 at 12:29












this problem was at romanian math olympiad - the local stage subject
– mathematiciangrade8
Jul 30 at 12:35




this problem was at romanian math olympiad - the local stage subject
– mathematiciangrade8
Jul 30 at 12:35












Do you use $[x]$ as the floor function or the nearest integer?
– kvantour
Jul 30 at 12:40




Do you use $[x]$ as the floor function or the nearest integer?
– kvantour
Jul 30 at 12:40












nearest integer
– mathematiciangrade8
Jul 30 at 12:40




nearest integer
– mathematiciangrade8
Jul 30 at 12:40










2 Answers
2






active

oldest

votes

















up vote
2
down vote













Let $k$ be such an integer, that $$k^2leq n< (k+1)^2implies [sqrtn]=k$$



So $[sqrtn+1] in k,k+1$.



Case 1: $[sqrtn+1] =k$ then we have $kmid n+2017$ and $kmid n+2018$ so $$kmid (n+2018)-(n+2017)=1implies k=1$$
Thus $1leq nleq 3$...(easy to check which one is good)



Case 2: $[sqrtn+1] =k+1$ then we have $n = k^2+2k$ and so $$k+1mid k^2+2k+2017 = (k+1)^2+2016implies k+1mid 2016;;;;(*)$$ and $$kmid k^2+2k+2018 implies kmid 2018 implies kin1,2,1009,2018$$



Because of $(*)$ $1009$ and $2018$ clearly doesn't work.



So the solution are $n=1,2,3,8$.






share|cite|improve this answer























  • i found that n=8 it respects
    – mathematiciangrade8
    Jul 30 at 12:31










  • Yes, I made an edit. If $k=2$ then $n=4+4=8$.
    – greedoid
    Jul 30 at 12:32










  • finally, u can write all solutions for n
    – mathematiciangrade8
    Jul 30 at 12:38










  • i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
    – mathematiciangrade8
    Jul 30 at 12:43










  • for example n=5 it respects the problem properties
    – mathematiciangrade8
    Jul 30 at 12:43

















up vote
1
down vote













Let $t:=lfloor sqrtnrfloor$. Clearly, $tleq lfloor sqrtn+1rfloor leq t+1$. If $lfloor sqrtn+1rfloor=t$, then $tmid n+2017$ and $tmid n+2018$ implies that $tmid 1$, whence $t=1$. That is, $nin1,2$.



If $lfloorsqrtn+1rfloor=t+1$, then $n=(t+1)^2-1$. Thus, $$t+1mid n+2017=(t+1)^2+2016text and tmid n+2018=(t+1)^2+2017,$$




That is, $t+1mid 2016$ and $tmid 2018$. Since the divisors of $2018$ are $1$, $2$, $1009$, and $2018$, we conclude that $tin1,2,1009,2018$. What next?







share|cite|improve this answer






























    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes








    up vote
    2
    down vote













    Let $k$ be such an integer, that $$k^2leq n< (k+1)^2implies [sqrtn]=k$$



    So $[sqrtn+1] in k,k+1$.



    Case 1: $[sqrtn+1] =k$ then we have $kmid n+2017$ and $kmid n+2018$ so $$kmid (n+2018)-(n+2017)=1implies k=1$$
    Thus $1leq nleq 3$...(easy to check which one is good)



    Case 2: $[sqrtn+1] =k+1$ then we have $n = k^2+2k$ and so $$k+1mid k^2+2k+2017 = (k+1)^2+2016implies k+1mid 2016;;;;(*)$$ and $$kmid k^2+2k+2018 implies kmid 2018 implies kin1,2,1009,2018$$



    Because of $(*)$ $1009$ and $2018$ clearly doesn't work.



    So the solution are $n=1,2,3,8$.






    share|cite|improve this answer























    • i found that n=8 it respects
      – mathematiciangrade8
      Jul 30 at 12:31










    • Yes, I made an edit. If $k=2$ then $n=4+4=8$.
      – greedoid
      Jul 30 at 12:32










    • finally, u can write all solutions for n
      – mathematiciangrade8
      Jul 30 at 12:38










    • i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
      – mathematiciangrade8
      Jul 30 at 12:43










    • for example n=5 it respects the problem properties
      – mathematiciangrade8
      Jul 30 at 12:43














    up vote
    2
    down vote













    Let $k$ be such an integer, that $$k^2leq n< (k+1)^2implies [sqrtn]=k$$



    So $[sqrtn+1] in k,k+1$.



    Case 1: $[sqrtn+1] =k$ then we have $kmid n+2017$ and $kmid n+2018$ so $$kmid (n+2018)-(n+2017)=1implies k=1$$
    Thus $1leq nleq 3$...(easy to check which one is good)



    Case 2: $[sqrtn+1] =k+1$ then we have $n = k^2+2k$ and so $$k+1mid k^2+2k+2017 = (k+1)^2+2016implies k+1mid 2016;;;;(*)$$ and $$kmid k^2+2k+2018 implies kmid 2018 implies kin1,2,1009,2018$$



    Because of $(*)$ $1009$ and $2018$ clearly doesn't work.



    So the solution are $n=1,2,3,8$.






    share|cite|improve this answer























    • i found that n=8 it respects
      – mathematiciangrade8
      Jul 30 at 12:31










    • Yes, I made an edit. If $k=2$ then $n=4+4=8$.
      – greedoid
      Jul 30 at 12:32










    • finally, u can write all solutions for n
      – mathematiciangrade8
      Jul 30 at 12:38










    • i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
      – mathematiciangrade8
      Jul 30 at 12:43










    • for example n=5 it respects the problem properties
      – mathematiciangrade8
      Jul 30 at 12:43












    up vote
    2
    down vote










    up vote
    2
    down vote









    Let $k$ be such an integer, that $$k^2leq n< (k+1)^2implies [sqrtn]=k$$



    So $[sqrtn+1] in k,k+1$.



    Case 1: $[sqrtn+1] =k$ then we have $kmid n+2017$ and $kmid n+2018$ so $$kmid (n+2018)-(n+2017)=1implies k=1$$
    Thus $1leq nleq 3$...(easy to check which one is good)



    Case 2: $[sqrtn+1] =k+1$ then we have $n = k^2+2k$ and so $$k+1mid k^2+2k+2017 = (k+1)^2+2016implies k+1mid 2016;;;;(*)$$ and $$kmid k^2+2k+2018 implies kmid 2018 implies kin1,2,1009,2018$$



    Because of $(*)$ $1009$ and $2018$ clearly doesn't work.



    So the solution are $n=1,2,3,8$.






    share|cite|improve this answer















    Let $k$ be such an integer, that $$k^2leq n< (k+1)^2implies [sqrtn]=k$$



    So $[sqrtn+1] in k,k+1$.



    Case 1: $[sqrtn+1] =k$ then we have $kmid n+2017$ and $kmid n+2018$ so $$kmid (n+2018)-(n+2017)=1implies k=1$$
    Thus $1leq nleq 3$...(easy to check which one is good)



    Case 2: $[sqrtn+1] =k+1$ then we have $n = k^2+2k$ and so $$k+1mid k^2+2k+2017 = (k+1)^2+2016implies k+1mid 2016;;;;(*)$$ and $$kmid k^2+2k+2018 implies kmid 2018 implies kin1,2,1009,2018$$



    Because of $(*)$ $1009$ and $2018$ clearly doesn't work.



    So the solution are $n=1,2,3,8$.







    share|cite|improve this answer















    share|cite|improve this answer



    share|cite|improve this answer








    edited Jul 30 at 12:41


























    answered Jul 30 at 12:17









    greedoid

    26.1k93473




    26.1k93473











    • i found that n=8 it respects
      – mathematiciangrade8
      Jul 30 at 12:31










    • Yes, I made an edit. If $k=2$ then $n=4+4=8$.
      – greedoid
      Jul 30 at 12:32










    • finally, u can write all solutions for n
      – mathematiciangrade8
      Jul 30 at 12:38










    • i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
      – mathematiciangrade8
      Jul 30 at 12:43










    • for example n=5 it respects the problem properties
      – mathematiciangrade8
      Jul 30 at 12:43
















    • i found that n=8 it respects
      – mathematiciangrade8
      Jul 30 at 12:31










    • Yes, I made an edit. If $k=2$ then $n=4+4=8$.
      – greedoid
      Jul 30 at 12:32










    • finally, u can write all solutions for n
      – mathematiciangrade8
      Jul 30 at 12:38










    • i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
      – mathematiciangrade8
      Jul 30 at 12:43










    • for example n=5 it respects the problem properties
      – mathematiciangrade8
      Jul 30 at 12:43















    i found that n=8 it respects
    – mathematiciangrade8
    Jul 30 at 12:31




    i found that n=8 it respects
    – mathematiciangrade8
    Jul 30 at 12:31












    Yes, I made an edit. If $k=2$ then $n=4+4=8$.
    – greedoid
    Jul 30 at 12:32




    Yes, I made an edit. If $k=2$ then $n=4+4=8$.
    – greedoid
    Jul 30 at 12:32












    finally, u can write all solutions for n
    – mathematiciangrade8
    Jul 30 at 12:38




    finally, u can write all solutions for n
    – mathematiciangrade8
    Jul 30 at 12:38












    i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
    – mathematiciangrade8
    Jul 30 at 12:43




    i found that solution but i forgot to say that the fractions over the problem can be natural numbers but not togheter at once!
    – mathematiciangrade8
    Jul 30 at 12:43












    for example n=5 it respects the problem properties
    – mathematiciangrade8
    Jul 30 at 12:43




    for example n=5 it respects the problem properties
    – mathematiciangrade8
    Jul 30 at 12:43










    up vote
    1
    down vote













    Let $t:=lfloor sqrtnrfloor$. Clearly, $tleq lfloor sqrtn+1rfloor leq t+1$. If $lfloor sqrtn+1rfloor=t$, then $tmid n+2017$ and $tmid n+2018$ implies that $tmid 1$, whence $t=1$. That is, $nin1,2$.



    If $lfloorsqrtn+1rfloor=t+1$, then $n=(t+1)^2-1$. Thus, $$t+1mid n+2017=(t+1)^2+2016text and tmid n+2018=(t+1)^2+2017,$$




    That is, $t+1mid 2016$ and $tmid 2018$. Since the divisors of $2018$ are $1$, $2$, $1009$, and $2018$, we conclude that $tin1,2,1009,2018$. What next?







    share|cite|improve this answer



























      up vote
      1
      down vote













      Let $t:=lfloor sqrtnrfloor$. Clearly, $tleq lfloor sqrtn+1rfloor leq t+1$. If $lfloor sqrtn+1rfloor=t$, then $tmid n+2017$ and $tmid n+2018$ implies that $tmid 1$, whence $t=1$. That is, $nin1,2$.



      If $lfloorsqrtn+1rfloor=t+1$, then $n=(t+1)^2-1$. Thus, $$t+1mid n+2017=(t+1)^2+2016text and tmid n+2018=(t+1)^2+2017,$$




      That is, $t+1mid 2016$ and $tmid 2018$. Since the divisors of $2018$ are $1$, $2$, $1009$, and $2018$, we conclude that $tin1,2,1009,2018$. What next?







      share|cite|improve this answer

























        up vote
        1
        down vote










        up vote
        1
        down vote









        Let $t:=lfloor sqrtnrfloor$. Clearly, $tleq lfloor sqrtn+1rfloor leq t+1$. If $lfloor sqrtn+1rfloor=t$, then $tmid n+2017$ and $tmid n+2018$ implies that $tmid 1$, whence $t=1$. That is, $nin1,2$.



        If $lfloorsqrtn+1rfloor=t+1$, then $n=(t+1)^2-1$. Thus, $$t+1mid n+2017=(t+1)^2+2016text and tmid n+2018=(t+1)^2+2017,$$




        That is, $t+1mid 2016$ and $tmid 2018$. Since the divisors of $2018$ are $1$, $2$, $1009$, and $2018$, we conclude that $tin1,2,1009,2018$. What next?







        share|cite|improve this answer















        Let $t:=lfloor sqrtnrfloor$. Clearly, $tleq lfloor sqrtn+1rfloor leq t+1$. If $lfloor sqrtn+1rfloor=t$, then $tmid n+2017$ and $tmid n+2018$ implies that $tmid 1$, whence $t=1$. That is, $nin1,2$.



        If $lfloorsqrtn+1rfloor=t+1$, then $n=(t+1)^2-1$. Thus, $$t+1mid n+2017=(t+1)^2+2016text and tmid n+2018=(t+1)^2+2017,$$




        That is, $t+1mid 2016$ and $tmid 2018$. Since the divisors of $2018$ are $1$, $2$, $1009$, and $2018$, we conclude that $tin1,2,1009,2018$. What next?








        share|cite|improve this answer















        share|cite|improve this answer



        share|cite|improve this answer








        edited Jul 30 at 12:35


























        answered Jul 30 at 12:29









        Batominovski

        22.9k22777




        22.9k22777












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