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 A118253 #19 Feb 16 2025 08:33:01
%S A118253 1,8,0,5,5,0,5,4,1,8,4,9,8,5,1,9,2,3,9,1,2,3,7,2,5,9,2,9,3,0,5,0,6,0,
%T A118253 7,5,9,1,1,3,4,0,2,3,5,8,0,5,6,1,8,3,9,5,4,1,2,3,5,9,9,9,2,2,1,7,6,6,
%U A118253 3,1,8,4,5,9,3,0,6,2,0,7,3,5,0,6,0,6,6,2,7,3,3,1,1,0,6,8,7,6,0,2,9,2
%N A118253 Decimal expansion of Product_{k>=1} sinc(2Pi/(2k+1)).
%D A118253 A. P. Prudnikov, Yu. A. Brychkov, and O. I. Marichev, Integrals and Series, Vol. 1 (Overseas Publishers Association, Amsterdam, 1986), p. 757, section 6.2.4, formula 2.
%H A118253 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SincFunction.html">Sinc Function</a>
%F A118253 Pi/(2K), where K is given by A051762.
%e A118253 0.180550541849851923912372592930506075911340235805618395412359992217663184593...
%p A118253 evalf(Pi/(2*(product(sec(Pi/k), k = 3..infinity))), 104); # _Vaclav Kotesovec_, Aug 16 2015
%t A118253 digits = 102; $MaxExtraPrecision = 100; exactEnd = 100; seriesOrder = 60; f[n_] := Log[Sinc[2Pi/(2n + 1)]]; exactSum = Sum[f[n], {n, 1, exactEnd}]; se = Series[f[n], {n, Infinity, seriesOrder}] // Normal; extraSum = Sum[se, {n, exactEnd + 1, Infinity}]; RealDigits[Exp[exactSum + extraSum ], 10, digits] // First (* _Jean-François Alcover_, Feb 07 2013 *)
%Y A118253 Cf. A051762.
%K A118253 nonn,cons
%O A118253 0,2
%A A118253 _Eric W. Weisstein_, Apr 18 2006
%E A118253 Last digit corrected by _Vaclav Kotesovec_, Aug 16 2015