■素数がもたらしたもの(その17)

 オイラー・マクローリンの和公式を

  Σ1/k^3

について適用してみたい.

  f(x)=1/x^3    f^(5)(x)=−7!/2x^8

  f’(x)=−3/x^4    f^(6)(x)=8!/2x^9

  f”(x)=12/x^5    f^(7)(x)=−9!/x^10

  f^(3)(x)=−60/x^6  f^(8)(x)=10!/x^11

  f^(4)(x)=360/x^7  f^(9)(x)=−11!/x^12

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  Σ(1,n)1/k^3〜∫(1,n)1/x^3dx+(f(n)+f(1))/2+ΣB2k/(2k)!(f^(2k-1)(n)-f^(2k-1)(1))+R

  ∫(1,n)1/x^3dx=[-1/2x^2]=-1/2n^2+1/2

  (f(n)+f(1))/2=(1/n^3+1)/2

  (f'(n)-f'(1))/12=(-3/n^4+3)/12

  (f^(3)(n)-f^(3)(1))/720=(-60/n^6+60)/720

  (f^(5)(n)-f^(5)(1))/30240=(-2520/n^7+2520)/30240

  (f^(7)(n)-f^(7)(1))/1209600=(-181440/n^9+181440)/1209600

  Σ1/k^3〜-1/2n^2+1/2n^3-1/4n^4+1/12n^8+・・・+1/2+1/2+1/4-1/12+R

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

  1+1/2^3 =1.125

  1+1/2^3+1/3^3 =1.16204

  1+1/2^3+1/3^3+1/4^3 =1.17766

  1+1/2^3+1/3^3+1/4^3+1/5^3 =1.18566

  1+1/2^3+1/3^3+1/4^3+1/5^3+1/6^3 =1.19029

  1+1/2^3+1/3^3+1/4^3+1/5^3+1/6^3+1/7^3 =1.19321

  1+1/2^3+1/3^3+1/4^3+1/5^3+1/6^3+1/7^3+1/8^3 =1.19516

  1+1/2^3+1/3^3+1/4^3+1/5^3+1/6^3+1/7^3+1/8^3+1/9^3 =1.19653

  1+1/2^3+1/3^3+1/4^3+1/5^3+1/6^3+1/7^3+1/8^3+1/9^3+1/10^3=1.19753

  1/2+1/2+1/4-1/12=1.16667

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