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 A261805 #15 Feb 16 2025 08:33:27 %S A261805 2,0,5,2,4,6,6,8,2,7,2,6,9,2,7,1,2,2,8,1,7,6,3,3,7,7,9,9,1,7,3,3,8,3, %T A261805 9,9,1,7,0,8,3,7,7,5,2,9,9,6,5,5,8,2,1,9,3,2,3,7,3,2,4,5,7,7,5,3,4,9, %U A261805 9,4,1,3,2,8,7,5,2,7,0,6,1,4,6,9,8,5,1,9,8,8,3,9,4,1,3,1,7,5,1,0,8,8,1 %N A261805 Decimal expansion of M_8, the 8th Madelung constant (negated). %D A261805 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 77. %H A261805 G. C. Greubel, <a href="/A261805/b261805.txt">Table of n, a(n) for n = 1..5000</a> %H A261805 Eric Weisstein's MathWorld, <a href="https://mathworld.wolfram.com/MadelungConstants.html">Madelung Constants</a> %F A261805 M_8 = (15/(4*Pi^3))*(8*sqrt(2) - 1)*zeta(1/2)*zeta(7/2). %e A261805 -2.052466827269271228176337799173383991708377529965582... %t A261805 M8 = (15/(4*Pi^3))*(8*Sqrt[2] - 1)*Zeta[1/2]*Zeta[7/2]; RealDigits[M8, 10, 103] // First %o A261805 (PARI) th4(x)=1+2*sumalt(n=1, (-1)^n*x^n^2) %o A261805 intnum(x=0, [oo, 1], (th4(exp(-x))^8-1)/sqrt(Pi*x)) \\ _Charles R Greathouse IV_, Jun 06 2016 %Y A261805 Cf. A059750, A088537, A085469, A090734, A247040, A261804. %K A261805 nonn,cons,easy %O A261805 1,1 %A A261805 _Jean-François Alcover_, Sep 01 2015