■BBP公式(その7)

  Sj=Σ1/(8n+j)

とおくと

 π=4S1-2S4-S5-S6

 また,1の8乗根をζ=(1+i)/√2として,

  Lj=ln(1-ζ^j/√2)

とおくと,

  L0=ln(1-1/√2)

  L1=1/2ln(1/2)-iarctan1=L7~

  L2=1/2ln(3/2)-iarctan(1//√2)=L6~

  L3=1/2ln(5/2)-iarctan(1/3)=L5~

  L4=ln(1+1/√2)

 -Sj/2^j/2=1/8(L0+L1/ζ^j+L2/ζ^2j+L3/ζ^3j+L4/ζ^4j+L5/ζ^5j+L6/ζ^6j+L7/ζ^7j)

 π=4S1-2S4-S5-S6=2L0-(2-2i)L1+2L4+(2+2i)L7

 ln2=S2+S4/2+S6/4+S8/8

 ln3=2S2+S6/2

 ln5=2S2+2S4+S6/2

 √2ln(√2+1)=S1+S3/2+S5/4+S7/8

 √2arctan(1/√2)=S1-S3/2+S5/4-S7/8

 arctan(1/3)=S1-S2-S4/2-S5/4

 0=8S1-8S2-4S3-8S4-2S5-2S6+S7

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  A=1/8ln(1+z)/(1-z)

  B=1/2^7/2ln(1+√2z+z^2)/(1-√2z+z^2)

  C=1/4arctan(z)

  D=1/2^5/2arctan(√2z/(1-z^2))

  Σz^8n+1/(8n+1)=A+B+C+D

  Σz^8n+3/(8n+3)=A-B-C+D

  Σz^8n+5/(8n+5)=A-B+C-D

  Σz^8n+7/(8n+7)=A+B-C-D

 一般に

  Σz^mn+a/(mn+a)

=-1/m{ln(1-z)+(-1)^a(m even)ln(1+z)+f(z))

f(z)=Σcos2πna/m・ln(1-2zcos2πn/m+z^2)-2sin2πna/m・arctan(zsin(2πn/m)/(1-zcos)2πn/m))

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