This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A264157 #20 Mar 05 2025 01:11:38
%S A264157 2,0,1,2,4,0,5,9,8,9,7,9,7,9,8,6,0,6,4,3,9,5,0,3,0,6,3,5,8,0,4,3,0,0,
%T A264157 4,4,1,6,5,6,7,8,0,6,5,8,1,2,1,9,2,9,3,2,8,7,8,4,9,0,4,6,9,1,1,7,3
%N A264157 Decimal expansion of M_7, the 7-dimensional analog of Madelung's constant (negated).
%D A264157 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 77.
%H A264157 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MadelungConstants.html">Madelung Constants</a>.
%F A264157 Equals (1/sqrt(Pi))*Integral_{t=0..oo} ((Sum_{k=-oo..oo} (-1)^k*exp(-k^2*t))^7-1)/sqrt(t) dt.
%e A264157 -2.01240598979798606439503063580430044165678065812192932878490469117330...
%t A264157 digits = 32; f[n_, x_] := 1/Sqrt[Pi*x]*(EllipticTheta[4, 0, Exp[-x]]^n - 1); M[7] = NIntegrate[f[7, x], {x, 0, Infinity}, WorkingPrecision -> digits + 5]; RealDigits[M[7], 10, digits] // First
%o A264157 (PARI) th4(x)=1+2*sumalt(n=1,(-1)^n*x^n^2)
%o A264157 intnum(x=0,[oo,1], (th4(exp(-x))^7-1)/sqrt(Pi*x)) \\ _Charles R Greathouse IV_, Jun 06 2016
%Y A264157 Cf. A088537, A085469, A090734, A247040, A261805, A264156.
%K A264157 nonn,cons
%O A264157 1,1
%A A264157 _Jean-François Alcover_, Nov 06 2015
%E A264157 More terms from _Charles R Greathouse IV_, Jun 06 2016