等比数列求和,首项为1,公比为2,总共64项,和为:1*(1-2^64)/(1-2)=2^64-1
2的64次方减一=18446744073709551615
S= 1+2^1+2^2+......+2^63 (1)2S= 2^1+2^2+2^3+......+2^64 (2)(2)-(1)S = 2^64 -11+2^1+2^2+......+2^63 = S = 2^64 -1