Does this series converges to some constant? [closed]

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Let $S = sum_i=1^log n fraci2^i$



Question : What is $S$ when $n$ tends to infinity? Is it a constant or some function of $n$?







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closed as unclear what you're asking by Jam, Simply Beautiful Art, user 108128, RRL, Key Flex Aug 2 at 14:29


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.














  • To me it appears to be something like $O(fraclognn)$.
    – old
    Aug 2 at 12:01






  • 3




    If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
    – Arthur
    Aug 2 at 12:01







  • 2




    The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
    – Peter
    Aug 2 at 12:01






  • 1




    I am fine with Order notation also.
    – lovw
    Aug 2 at 12:01






  • 3




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
    – Eff
    Aug 2 at 12:05














up vote
0
down vote

favorite
3












Let $S = sum_i=1^log n fraci2^i$



Question : What is $S$ when $n$ tends to infinity? Is it a constant or some function of $n$?







share|cite|improve this question













closed as unclear what you're asking by Jam, Simply Beautiful Art, user 108128, RRL, Key Flex Aug 2 at 14:29


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.














  • To me it appears to be something like $O(fraclognn)$.
    – old
    Aug 2 at 12:01






  • 3




    If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
    – Arthur
    Aug 2 at 12:01







  • 2




    The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
    – Peter
    Aug 2 at 12:01






  • 1




    I am fine with Order notation also.
    – lovw
    Aug 2 at 12:01






  • 3




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
    – Eff
    Aug 2 at 12:05












up vote
0
down vote

favorite
3









up vote
0
down vote

favorite
3






3





Let $S = sum_i=1^log n fraci2^i$



Question : What is $S$ when $n$ tends to infinity? Is it a constant or some function of $n$?







share|cite|improve this question













Let $S = sum_i=1^log n fraci2^i$



Question : What is $S$ when $n$ tends to infinity? Is it a constant or some function of $n$?









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Aug 2 at 12:34









BCLC

6,98221973




6,98221973









asked Aug 2 at 11:58









lovw

224




224




closed as unclear what you're asking by Jam, Simply Beautiful Art, user 108128, RRL, Key Flex Aug 2 at 14:29


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.






closed as unclear what you're asking by Jam, Simply Beautiful Art, user 108128, RRL, Key Flex Aug 2 at 14:29


Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.













  • To me it appears to be something like $O(fraclognn)$.
    – old
    Aug 2 at 12:01






  • 3




    If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
    – Arthur
    Aug 2 at 12:01







  • 2




    The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
    – Peter
    Aug 2 at 12:01






  • 1




    I am fine with Order notation also.
    – lovw
    Aug 2 at 12:01






  • 3




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
    – Eff
    Aug 2 at 12:05
















  • To me it appears to be something like $O(fraclognn)$.
    – old
    Aug 2 at 12:01






  • 3




    If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
    – Arthur
    Aug 2 at 12:01







  • 2




    The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
    – Peter
    Aug 2 at 12:01






  • 1




    I am fine with Order notation also.
    – lovw
    Aug 2 at 12:01






  • 3




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
    – Eff
    Aug 2 at 12:05















To me it appears to be something like $O(fraclognn)$.
– old
Aug 2 at 12:01




To me it appears to be something like $O(fraclognn)$.
– old
Aug 2 at 12:01




3




3




If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
– Arthur
Aug 2 at 12:01





If we let $n$ tend to infinity, the resulting value can't really depend on $n$.
– Arthur
Aug 2 at 12:01





2




2




The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
– Peter
Aug 2 at 12:01




The upper limit should be a natural number. Do you mean perhaps $lfloor log nrfloor$ ?
– Peter
Aug 2 at 12:01




1




1




I am fine with Order notation also.
– lovw
Aug 2 at 12:01




I am fine with Order notation also.
– lovw
Aug 2 at 12:01




3




3




I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
– Eff
Aug 2 at 12:05




I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$.
– Eff
Aug 2 at 12:05










3 Answers
3






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up vote
4
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If you mean$$sum_i=1^lfloor log nrfloorfrac i2^i,$$then what you haee is a subsequence of the sequence$$left(sum_i=1^nfrac i2^iright)_ninmathbb N,$$whose sum is $2$. Therefore, the limit of your sequence is $2$, too.






share|cite|improve this answer

















  • 4




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
    – Eff
    Aug 2 at 12:06






  • 2




    @Elf Let us wait and see what the OP has to say about that.
    – José Carlos Santos
    Aug 2 at 12:07

















up vote
1
down vote













Consider for $|x|<1$



$$frac ddxsum_i=0^infty x^i=sum_i=1^infty ix^(i-1)=frac ddxleft(frac11-xright)=frac1(1-x)^2$$



then



$$sum_i=1^infty ix^i=xsum_i=1^infty ix^(i-1)=fracx(1-x)^2$$



therefore



$$sum_i=1^inftyfrac i2^i=2$$



and then



$$lim_nto infty sum_i=1^lfloor log nrfloorfrac i2^i=2$$



For the asymptotic grow we have that



$$frac ddxsum_i=0^N x^i=sum_i=1^N ix^(i-1)=frac ddxleft(frac1-x^N+11-xright)=frac1(1-x)^2-fracx^N(1-x)^2(1+N-Nx)$$



and then



$$sum_i=1^N ix^i=xsum_i=1^N ix^(i-1)=fracx(1-x)^2-fracx(1-x)^2x^N(1+N-Nx)$$



and then for $x=frac12$



$$sum_i=1^Nfrac i2^i=2-2frac12^Nleft(1+frac N 2right)=2-frac22^N-fracN2^N=2+Oleft(fracN2^Nright)$$






share|cite|improve this answer























  • @lovw If the value of the limit is not what you want, then you should be clearer in the question
    – Calvin Khor
    Aug 2 at 12:07

















up vote
1
down vote













Hint. Show by induction that for $Ngeq 1$,
$$sum_i=1^N fraci2^i=2-fracN+22^N.$$
Then the asymptotic growth is
$$S(n)=sum_i=1^lfloor log nrfloor fraci2^i=2-fraclfloor log nrfloor+22^lfloor log nrfloorsim 2-fraclog nn^log 2.$$






share|cite|improve this answer






























    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes








    up vote
    4
    down vote













    If you mean$$sum_i=1^lfloor log nrfloorfrac i2^i,$$then what you haee is a subsequence of the sequence$$left(sum_i=1^nfrac i2^iright)_ninmathbb N,$$whose sum is $2$. Therefore, the limit of your sequence is $2$, too.






    share|cite|improve this answer

















    • 4




      I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
      – Eff
      Aug 2 at 12:06






    • 2




      @Elf Let us wait and see what the OP has to say about that.
      – José Carlos Santos
      Aug 2 at 12:07














    up vote
    4
    down vote













    If you mean$$sum_i=1^lfloor log nrfloorfrac i2^i,$$then what you haee is a subsequence of the sequence$$left(sum_i=1^nfrac i2^iright)_ninmathbb N,$$whose sum is $2$. Therefore, the limit of your sequence is $2$, too.






    share|cite|improve this answer

















    • 4




      I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
      – Eff
      Aug 2 at 12:06






    • 2




      @Elf Let us wait and see what the OP has to say about that.
      – José Carlos Santos
      Aug 2 at 12:07












    up vote
    4
    down vote










    up vote
    4
    down vote









    If you mean$$sum_i=1^lfloor log nrfloorfrac i2^i,$$then what you haee is a subsequence of the sequence$$left(sum_i=1^nfrac i2^iright)_ninmathbb N,$$whose sum is $2$. Therefore, the limit of your sequence is $2$, too.






    share|cite|improve this answer













    If you mean$$sum_i=1^lfloor log nrfloorfrac i2^i,$$then what you haee is a subsequence of the sequence$$left(sum_i=1^nfrac i2^iright)_ninmathbb N,$$whose sum is $2$. Therefore, the limit of your sequence is $2$, too.







    share|cite|improve this answer













    share|cite|improve this answer



    share|cite|improve this answer











    answered Aug 2 at 12:03









    José Carlos Santos

    112k1696172




    112k1696172







    • 4




      I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
      – Eff
      Aug 2 at 12:06






    • 2




      @Elf Let us wait and see what the OP has to say about that.
      – José Carlos Santos
      Aug 2 at 12:07












    • 4




      I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
      – Eff
      Aug 2 at 12:06






    • 2




      @Elf Let us wait and see what the OP has to say about that.
      – José Carlos Santos
      Aug 2 at 12:07







    4




    4




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
    – Eff
    Aug 2 at 12:06




    I think the OP is not looking for the limit per se, but the asymptotic growth of $S(n)$, i.e. with respect to $n$. However, I might be mistaken.
    – Eff
    Aug 2 at 12:06




    2




    2




    @Elf Let us wait and see what the OP has to say about that.
    – José Carlos Santos
    Aug 2 at 12:07




    @Elf Let us wait and see what the OP has to say about that.
    – José Carlos Santos
    Aug 2 at 12:07










    up vote
    1
    down vote













    Consider for $|x|<1$



    $$frac ddxsum_i=0^infty x^i=sum_i=1^infty ix^(i-1)=frac ddxleft(frac11-xright)=frac1(1-x)^2$$



    then



    $$sum_i=1^infty ix^i=xsum_i=1^infty ix^(i-1)=fracx(1-x)^2$$



    therefore



    $$sum_i=1^inftyfrac i2^i=2$$



    and then



    $$lim_nto infty sum_i=1^lfloor log nrfloorfrac i2^i=2$$



    For the asymptotic grow we have that



    $$frac ddxsum_i=0^N x^i=sum_i=1^N ix^(i-1)=frac ddxleft(frac1-x^N+11-xright)=frac1(1-x)^2-fracx^N(1-x)^2(1+N-Nx)$$



    and then



    $$sum_i=1^N ix^i=xsum_i=1^N ix^(i-1)=fracx(1-x)^2-fracx(1-x)^2x^N(1+N-Nx)$$



    and then for $x=frac12$



    $$sum_i=1^Nfrac i2^i=2-2frac12^Nleft(1+frac N 2right)=2-frac22^N-fracN2^N=2+Oleft(fracN2^Nright)$$






    share|cite|improve this answer























    • @lovw If the value of the limit is not what you want, then you should be clearer in the question
      – Calvin Khor
      Aug 2 at 12:07














    up vote
    1
    down vote













    Consider for $|x|<1$



    $$frac ddxsum_i=0^infty x^i=sum_i=1^infty ix^(i-1)=frac ddxleft(frac11-xright)=frac1(1-x)^2$$



    then



    $$sum_i=1^infty ix^i=xsum_i=1^infty ix^(i-1)=fracx(1-x)^2$$



    therefore



    $$sum_i=1^inftyfrac i2^i=2$$



    and then



    $$lim_nto infty sum_i=1^lfloor log nrfloorfrac i2^i=2$$



    For the asymptotic grow we have that



    $$frac ddxsum_i=0^N x^i=sum_i=1^N ix^(i-1)=frac ddxleft(frac1-x^N+11-xright)=frac1(1-x)^2-fracx^N(1-x)^2(1+N-Nx)$$



    and then



    $$sum_i=1^N ix^i=xsum_i=1^N ix^(i-1)=fracx(1-x)^2-fracx(1-x)^2x^N(1+N-Nx)$$



    and then for $x=frac12$



    $$sum_i=1^Nfrac i2^i=2-2frac12^Nleft(1+frac N 2right)=2-frac22^N-fracN2^N=2+Oleft(fracN2^Nright)$$






    share|cite|improve this answer























    • @lovw If the value of the limit is not what you want, then you should be clearer in the question
      – Calvin Khor
      Aug 2 at 12:07












    up vote
    1
    down vote










    up vote
    1
    down vote









    Consider for $|x|<1$



    $$frac ddxsum_i=0^infty x^i=sum_i=1^infty ix^(i-1)=frac ddxleft(frac11-xright)=frac1(1-x)^2$$



    then



    $$sum_i=1^infty ix^i=xsum_i=1^infty ix^(i-1)=fracx(1-x)^2$$



    therefore



    $$sum_i=1^inftyfrac i2^i=2$$



    and then



    $$lim_nto infty sum_i=1^lfloor log nrfloorfrac i2^i=2$$



    For the asymptotic grow we have that



    $$frac ddxsum_i=0^N x^i=sum_i=1^N ix^(i-1)=frac ddxleft(frac1-x^N+11-xright)=frac1(1-x)^2-fracx^N(1-x)^2(1+N-Nx)$$



    and then



    $$sum_i=1^N ix^i=xsum_i=1^N ix^(i-1)=fracx(1-x)^2-fracx(1-x)^2x^N(1+N-Nx)$$



    and then for $x=frac12$



    $$sum_i=1^Nfrac i2^i=2-2frac12^Nleft(1+frac N 2right)=2-frac22^N-fracN2^N=2+Oleft(fracN2^Nright)$$






    share|cite|improve this answer















    Consider for $|x|<1$



    $$frac ddxsum_i=0^infty x^i=sum_i=1^infty ix^(i-1)=frac ddxleft(frac11-xright)=frac1(1-x)^2$$



    then



    $$sum_i=1^infty ix^i=xsum_i=1^infty ix^(i-1)=fracx(1-x)^2$$



    therefore



    $$sum_i=1^inftyfrac i2^i=2$$



    and then



    $$lim_nto infty sum_i=1^lfloor log nrfloorfrac i2^i=2$$



    For the asymptotic grow we have that



    $$frac ddxsum_i=0^N x^i=sum_i=1^N ix^(i-1)=frac ddxleft(frac1-x^N+11-xright)=frac1(1-x)^2-fracx^N(1-x)^2(1+N-Nx)$$



    and then



    $$sum_i=1^N ix^i=xsum_i=1^N ix^(i-1)=fracx(1-x)^2-fracx(1-x)^2x^N(1+N-Nx)$$



    and then for $x=frac12$



    $$sum_i=1^Nfrac i2^i=2-2frac12^Nleft(1+frac N 2right)=2-frac22^N-fracN2^N=2+Oleft(fracN2^Nright)$$







    share|cite|improve this answer















    share|cite|improve this answer



    share|cite|improve this answer








    edited Aug 2 at 13:19


























    answered Aug 2 at 12:01









    gimusi

    63.8k73480




    63.8k73480











    • @lovw If the value of the limit is not what you want, then you should be clearer in the question
      – Calvin Khor
      Aug 2 at 12:07
















    • @lovw If the value of the limit is not what you want, then you should be clearer in the question
      – Calvin Khor
      Aug 2 at 12:07















    @lovw If the value of the limit is not what you want, then you should be clearer in the question
    – Calvin Khor
    Aug 2 at 12:07




    @lovw If the value of the limit is not what you want, then you should be clearer in the question
    – Calvin Khor
    Aug 2 at 12:07










    up vote
    1
    down vote













    Hint. Show by induction that for $Ngeq 1$,
    $$sum_i=1^N fraci2^i=2-fracN+22^N.$$
    Then the asymptotic growth is
    $$S(n)=sum_i=1^lfloor log nrfloor fraci2^i=2-fraclfloor log nrfloor+22^lfloor log nrfloorsim 2-fraclog nn^log 2.$$






    share|cite|improve this answer



























      up vote
      1
      down vote













      Hint. Show by induction that for $Ngeq 1$,
      $$sum_i=1^N fraci2^i=2-fracN+22^N.$$
      Then the asymptotic growth is
      $$S(n)=sum_i=1^lfloor log nrfloor fraci2^i=2-fraclfloor log nrfloor+22^lfloor log nrfloorsim 2-fraclog nn^log 2.$$






      share|cite|improve this answer

























        up vote
        1
        down vote










        up vote
        1
        down vote









        Hint. Show by induction that for $Ngeq 1$,
        $$sum_i=1^N fraci2^i=2-fracN+22^N.$$
        Then the asymptotic growth is
        $$S(n)=sum_i=1^lfloor log nrfloor fraci2^i=2-fraclfloor log nrfloor+22^lfloor log nrfloorsim 2-fraclog nn^log 2.$$






        share|cite|improve this answer















        Hint. Show by induction that for $Ngeq 1$,
        $$sum_i=1^N fraci2^i=2-fracN+22^N.$$
        Then the asymptotic growth is
        $$S(n)=sum_i=1^lfloor log nrfloor fraci2^i=2-fraclfloor log nrfloor+22^lfloor log nrfloorsim 2-fraclog nn^log 2.$$







        share|cite|improve this answer















        share|cite|improve this answer



        share|cite|improve this answer








        edited Aug 2 at 14:39


























        answered Aug 2 at 12:35









        Robert Z

        83.5k954122




        83.5k954122












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