■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
===================================
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
===================================