The closed form for $sum_{ngeq1}frac1{n(n+1)(n+2)cdots(n+m)}$ [duplicate]












2












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This question already has an answer here:




  • Sum of infinite series $sum_{i=1}^{infty} frac 1 {i(i+1)(i+2)…(i+n)}$

    4 answers




Just for fun, I defined the following series. For $minBbb N$,
$$g_m=sum_{ngeq1}prod_{i=0}^{m}frac1{n+i}$$
I am seeking a closed form for $g_m$. I found $g_1, g_2$, and a general expression involving a lot of integrals.



$$
begin{align}
g_1=&sum_{ngeq1}frac1{n(n+1)}\
=&sum_{ngeq1}frac1nint_0^1 t_0^nmathrm{d}t_0\
=&sum_{ngeq1}int_0^1int_0^{t_0} t_1^{n-1}mathrm{d}t_1mathrm{d}t_0 \
=&int_0^1int_0^{t_0}sum_{ngeq0}t_1^{n}mathrm{d}t_1mathrm{d}t_0 \
=&int_0^1int_0^{t_0}frac{mathrm{d}t_1}{1-t_1}mathrm{d}t_0 \
=&1 \
end{align}
$$

Through the same process, it can be shown that $g_2=frac14$. In fact, through the same process, it can be shown that
$$g_m=int_0^1int_0^{t_0}int_0^{t_1}cdotsint_0^{t_{m-2}}frac{mathrm{d}t_{m-1}}{1-t_{m-1}}mathrm{d}t_{m-2}cdotsmathrm{d}t_2mathrm{d}t_1mathrm{d}t_0$$
Which I don't even know how to approach. Any ideas? Thanks.



This isn't a duplicate question, because I would like to know how to evaluate those nested integrals, if possible.










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marked as duplicate by Math Lover, Lord Shark the Unknown, user10354138, Masacroso, Brahadeesh Nov 27 '18 at 5:51


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.























    2












    $begingroup$



    This question already has an answer here:




    • Sum of infinite series $sum_{i=1}^{infty} frac 1 {i(i+1)(i+2)…(i+n)}$

      4 answers




    Just for fun, I defined the following series. For $minBbb N$,
    $$g_m=sum_{ngeq1}prod_{i=0}^{m}frac1{n+i}$$
    I am seeking a closed form for $g_m$. I found $g_1, g_2$, and a general expression involving a lot of integrals.



    $$
    begin{align}
    g_1=&sum_{ngeq1}frac1{n(n+1)}\
    =&sum_{ngeq1}frac1nint_0^1 t_0^nmathrm{d}t_0\
    =&sum_{ngeq1}int_0^1int_0^{t_0} t_1^{n-1}mathrm{d}t_1mathrm{d}t_0 \
    =&int_0^1int_0^{t_0}sum_{ngeq0}t_1^{n}mathrm{d}t_1mathrm{d}t_0 \
    =&int_0^1int_0^{t_0}frac{mathrm{d}t_1}{1-t_1}mathrm{d}t_0 \
    =&1 \
    end{align}
    $$

    Through the same process, it can be shown that $g_2=frac14$. In fact, through the same process, it can be shown that
    $$g_m=int_0^1int_0^{t_0}int_0^{t_1}cdotsint_0^{t_{m-2}}frac{mathrm{d}t_{m-1}}{1-t_{m-1}}mathrm{d}t_{m-2}cdotsmathrm{d}t_2mathrm{d}t_1mathrm{d}t_0$$
    Which I don't even know how to approach. Any ideas? Thanks.



    This isn't a duplicate question, because I would like to know how to evaluate those nested integrals, if possible.










    share|cite|improve this question











    $endgroup$



    marked as duplicate by Math Lover, Lord Shark the Unknown, user10354138, Masacroso, Brahadeesh Nov 27 '18 at 5:51


    This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.





















      2












      2








      2





      $begingroup$



      This question already has an answer here:




      • Sum of infinite series $sum_{i=1}^{infty} frac 1 {i(i+1)(i+2)…(i+n)}$

        4 answers




      Just for fun, I defined the following series. For $minBbb N$,
      $$g_m=sum_{ngeq1}prod_{i=0}^{m}frac1{n+i}$$
      I am seeking a closed form for $g_m$. I found $g_1, g_2$, and a general expression involving a lot of integrals.



      $$
      begin{align}
      g_1=&sum_{ngeq1}frac1{n(n+1)}\
      =&sum_{ngeq1}frac1nint_0^1 t_0^nmathrm{d}t_0\
      =&sum_{ngeq1}int_0^1int_0^{t_0} t_1^{n-1}mathrm{d}t_1mathrm{d}t_0 \
      =&int_0^1int_0^{t_0}sum_{ngeq0}t_1^{n}mathrm{d}t_1mathrm{d}t_0 \
      =&int_0^1int_0^{t_0}frac{mathrm{d}t_1}{1-t_1}mathrm{d}t_0 \
      =&1 \
      end{align}
      $$

      Through the same process, it can be shown that $g_2=frac14$. In fact, through the same process, it can be shown that
      $$g_m=int_0^1int_0^{t_0}int_0^{t_1}cdotsint_0^{t_{m-2}}frac{mathrm{d}t_{m-1}}{1-t_{m-1}}mathrm{d}t_{m-2}cdotsmathrm{d}t_2mathrm{d}t_1mathrm{d}t_0$$
      Which I don't even know how to approach. Any ideas? Thanks.



      This isn't a duplicate question, because I would like to know how to evaluate those nested integrals, if possible.










      share|cite|improve this question











      $endgroup$





      This question already has an answer here:




      • Sum of infinite series $sum_{i=1}^{infty} frac 1 {i(i+1)(i+2)…(i+n)}$

        4 answers




      Just for fun, I defined the following series. For $minBbb N$,
      $$g_m=sum_{ngeq1}prod_{i=0}^{m}frac1{n+i}$$
      I am seeking a closed form for $g_m$. I found $g_1, g_2$, and a general expression involving a lot of integrals.



      $$
      begin{align}
      g_1=&sum_{ngeq1}frac1{n(n+1)}\
      =&sum_{ngeq1}frac1nint_0^1 t_0^nmathrm{d}t_0\
      =&sum_{ngeq1}int_0^1int_0^{t_0} t_1^{n-1}mathrm{d}t_1mathrm{d}t_0 \
      =&int_0^1int_0^{t_0}sum_{ngeq0}t_1^{n}mathrm{d}t_1mathrm{d}t_0 \
      =&int_0^1int_0^{t_0}frac{mathrm{d}t_1}{1-t_1}mathrm{d}t_0 \
      =&1 \
      end{align}
      $$

      Through the same process, it can be shown that $g_2=frac14$. In fact, through the same process, it can be shown that
      $$g_m=int_0^1int_0^{t_0}int_0^{t_1}cdotsint_0^{t_{m-2}}frac{mathrm{d}t_{m-1}}{1-t_{m-1}}mathrm{d}t_{m-2}cdotsmathrm{d}t_2mathrm{d}t_1mathrm{d}t_0$$
      Which I don't even know how to approach. Any ideas? Thanks.



      This isn't a duplicate question, because I would like to know how to evaluate those nested integrals, if possible.





      This question already has an answer here:




      • Sum of infinite series $sum_{i=1}^{infty} frac 1 {i(i+1)(i+2)…(i+n)}$

        4 answers








      integration sequences-and-series






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      edited Nov 27 '18 at 5:34







      clathratus

















      asked Nov 27 '18 at 3:27









      clathratusclathratus

      3,767333




      3,767333




      marked as duplicate by Math Lover, Lord Shark the Unknown, user10354138, Masacroso, Brahadeesh Nov 27 '18 at 5:51


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.









      marked as duplicate by Math Lover, Lord Shark the Unknown, user10354138, Masacroso, Brahadeesh Nov 27 '18 at 5:51


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
























          2 Answers
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          The sum telescopes:
          $$frac{m}{x(x+1)cdots(x+m)}=frac1{x(x+1)cdots(x+m-1)}
          -frac1{(x+1)(x+2)cdots(x+m)}.$$

          Summing this from $1$ to $infty$ gives
          $$msum_{n=1}^inftyfrac{1}{n(n+1)cdots(n+m)}
          =frac1{(m-1)!}$$

          so your sum is $1/m!$.






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            1












            $begingroup$

            $sum_{n=1}^{infty}frac{1}{n(n+1)ldots(n+m)}=frac{1}{m}sum_{n=1}^{infty}(frac{1}{n(n+1)ldots(n+m-1)}-frac{1}{(n+1)(n+2)ldots(n+m)})$, which can be easily verified by adding the fractions. From here, you can define $V_{n}=frac{1}{n(n+1)ldots(n+m-1)}$, and so clearly



            $$g_m=frac{1}{m}sum_{n=1}^{infty}(V_n-V_{n+1})$$ and from here it is fairly obvious what to do






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              2 Answers
              2






              active

              oldest

              votes








              2 Answers
              2






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes









              1












              $begingroup$

              The sum telescopes:
              $$frac{m}{x(x+1)cdots(x+m)}=frac1{x(x+1)cdots(x+m-1)}
              -frac1{(x+1)(x+2)cdots(x+m)}.$$

              Summing this from $1$ to $infty$ gives
              $$msum_{n=1}^inftyfrac{1}{n(n+1)cdots(n+m)}
              =frac1{(m-1)!}$$

              so your sum is $1/m!$.






              share|cite|improve this answer











              $endgroup$


















                1












                $begingroup$

                The sum telescopes:
                $$frac{m}{x(x+1)cdots(x+m)}=frac1{x(x+1)cdots(x+m-1)}
                -frac1{(x+1)(x+2)cdots(x+m)}.$$

                Summing this from $1$ to $infty$ gives
                $$msum_{n=1}^inftyfrac{1}{n(n+1)cdots(n+m)}
                =frac1{(m-1)!}$$

                so your sum is $1/m!$.






                share|cite|improve this answer











                $endgroup$
















                  1












                  1








                  1





                  $begingroup$

                  The sum telescopes:
                  $$frac{m}{x(x+1)cdots(x+m)}=frac1{x(x+1)cdots(x+m-1)}
                  -frac1{(x+1)(x+2)cdots(x+m)}.$$

                  Summing this from $1$ to $infty$ gives
                  $$msum_{n=1}^inftyfrac{1}{n(n+1)cdots(n+m)}
                  =frac1{(m-1)!}$$

                  so your sum is $1/m!$.






                  share|cite|improve this answer











                  $endgroup$



                  The sum telescopes:
                  $$frac{m}{x(x+1)cdots(x+m)}=frac1{x(x+1)cdots(x+m-1)}
                  -frac1{(x+1)(x+2)cdots(x+m)}.$$

                  Summing this from $1$ to $infty$ gives
                  $$msum_{n=1}^inftyfrac{1}{n(n+1)cdots(n+m)}
                  =frac1{(m-1)!}$$

                  so your sum is $1/m!$.







                  share|cite|improve this answer














                  share|cite|improve this answer



                  share|cite|improve this answer








                  edited Nov 27 '18 at 4:06

























                  answered Nov 27 '18 at 3:39









                  Lord Shark the UnknownLord Shark the Unknown

                  103k1160132




                  103k1160132























                      1












                      $begingroup$

                      $sum_{n=1}^{infty}frac{1}{n(n+1)ldots(n+m)}=frac{1}{m}sum_{n=1}^{infty}(frac{1}{n(n+1)ldots(n+m-1)}-frac{1}{(n+1)(n+2)ldots(n+m)})$, which can be easily verified by adding the fractions. From here, you can define $V_{n}=frac{1}{n(n+1)ldots(n+m-1)}$, and so clearly



                      $$g_m=frac{1}{m}sum_{n=1}^{infty}(V_n-V_{n+1})$$ and from here it is fairly obvious what to do






                      share|cite|improve this answer











                      $endgroup$


















                        1












                        $begingroup$

                        $sum_{n=1}^{infty}frac{1}{n(n+1)ldots(n+m)}=frac{1}{m}sum_{n=1}^{infty}(frac{1}{n(n+1)ldots(n+m-1)}-frac{1}{(n+1)(n+2)ldots(n+m)})$, which can be easily verified by adding the fractions. From here, you can define $V_{n}=frac{1}{n(n+1)ldots(n+m-1)}$, and so clearly



                        $$g_m=frac{1}{m}sum_{n=1}^{infty}(V_n-V_{n+1})$$ and from here it is fairly obvious what to do






                        share|cite|improve this answer











                        $endgroup$
















                          1












                          1








                          1





                          $begingroup$

                          $sum_{n=1}^{infty}frac{1}{n(n+1)ldots(n+m)}=frac{1}{m}sum_{n=1}^{infty}(frac{1}{n(n+1)ldots(n+m-1)}-frac{1}{(n+1)(n+2)ldots(n+m)})$, which can be easily verified by adding the fractions. From here, you can define $V_{n}=frac{1}{n(n+1)ldots(n+m-1)}$, and so clearly



                          $$g_m=frac{1}{m}sum_{n=1}^{infty}(V_n-V_{n+1})$$ and from here it is fairly obvious what to do






                          share|cite|improve this answer











                          $endgroup$



                          $sum_{n=1}^{infty}frac{1}{n(n+1)ldots(n+m)}=frac{1}{m}sum_{n=1}^{infty}(frac{1}{n(n+1)ldots(n+m-1)}-frac{1}{(n+1)(n+2)ldots(n+m)})$, which can be easily verified by adding the fractions. From here, you can define $V_{n}=frac{1}{n(n+1)ldots(n+m-1)}$, and so clearly



                          $$g_m=frac{1}{m}sum_{n=1}^{infty}(V_n-V_{n+1})$$ and from here it is fairly obvious what to do







                          share|cite|improve this answer














                          share|cite|improve this answer



                          share|cite|improve this answer








                          edited Nov 27 '18 at 4:14









                          clathratus

                          3,767333




                          3,767333










                          answered Nov 27 '18 at 3:40









                          SethSeth

                          42812




                          42812















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