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 A257872 #31 Feb 16 2025 08:33:25
%S A257872 5,5,4,5,1,7,7,4,4,4,4,7,9,5,6,2,4,7,5,3,3,7,8,5,6,9,7,1,6,6,5,4,1,2,
%T A257872 5,4,4,6,0,4,0,0,1,0,7,4,8,8,2,0,4,2,0,3,2,9,6,5,4,4,0,0,7,5,9,4,7,1,
%U A257872 4,8,9,7,5,7,5,7,5,5,7,7,2,4,8,4,6,9,0,6,6,1,5,9,7,1,3,4,9,5,0,0,3,3,6
%N A257872 Decimal expansion of the Madelung type constant C(4|1) (negated).
%C A257872 Without sign, this is the volume of the intersection of the three (solid) hyperboloids x^2 + y^2 - z^2 <= 1; y^2 + z^2 - x^2 <= 1; z^2 + x^2 - y^2 <= 1. See Villarino et al. - _Michel Marcus_, Aug 12 2021
%C A257872 In other words, decimal expansion of the volume of the unit trihyperboloid. - _Eric W. Weisstein_, Sep 18 2021
%H A257872 Hassan Chamati and Nicholay S. Tonchev, <a href="http://arxiv.org/abs/cond-mat/0003235">Exact results for some Madelung type constants in the finite-size scaling theory</a>, arXiv:cond-mat/0003235 [cond-mat.stat-mech], 2000.
%H A257872 Mark B. Villarino and Joseph C. Várilly, <a href="https://arxiv.org/abs/2108.05195">Archimedes' Revenge</a>, arXiv:2108.05195 [math.HO], 2021.
%H A257872 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MadelungConstants.html">Madelung Constants</a>
%H A257872 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Trihyperboloid.html">Trihyperboloid</a>
%H A257872 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>
%F A257872 -8*log(2).
%F A257872 4*log(2)/5 = 8*log(2)/10 = Sum_{k>=1} F(k)^2/(k * 3^k), where F(k) is the k-th Fibonacci number (A000045). - _Amiram Eldar_, Aug 09 2020
%e A257872 -5.54517744447956247533785697166541254460400107488204203296544...
%p A257872 evalf(-8*log(2),120); # _Vaclav Kotesovec_, May 11 2015
%t A257872 RealDigits[-8*Log[2], 10, 103] // First
%o A257872 (PARI) -8*log(2) \\ _Charles R Greathouse IV_, Sep 02 2021
%Y A257872 Cf. A000045, A257870, A257871.
%Y A257872 Cf. A347903 (surface area of the unit trihyperboloid).
%K A257872 nonn,cons,easy
%O A257872 1,1
%A A257872 _Jean-François Alcover_, May 11 2015