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 A308642 #17 Sep 03 2025 09:13:52
%S A308642 3,4,0,8,4,3,7,9,5,2,6,8,8,4,9,9,1,2,5,0,9,7,2,5,6,8,9,4,3,0,4,2,0,6,
%T A308642 6,9,8,6,2,0,9,2,2,1,8,4,3,0,7,6,6,3,1,2,3,8,2,7,0,0,2,6,5,5,8,4,4,2,
%U A308642 5,0,1,9,9,6,3,5,8,9,0,8,0,0,9,0,2,8,6,4,3,4,2,5,3,3,9,6,0,0,1,5,7,2,4,1,2,2,2,2,5,6,0,1,4,0,6,7,8,3,9,7
%N A308642 Decimal expansion of cosh(sqrt(13/3)*Pi/2)*sech(sqrt(5/3)*Pi/2).
%H A308642 Kelvin Voskuijl, <a href="/A308642/b308642.txt">Table of n, a(n) for n = 1..20000</a>
%F A308642 Equals Product_{k>=1} (1 + 1/(3*k*(k - 1)/2 + 1)).
%F A308642 Equals Product_{k>=1} (1 + 1/A005448(k)).
%e A308642 3.4084379526884991250972568943042066986209221843076631...
%t A308642 RealDigits[Cosh[Sqrt[13/3] Pi/2] Sech[Sqrt[5/3] Pi/2], 10, 120][[1]]
%t A308642 RealDigits[Product[(1 + 1/(3 k (k - 1)/2 + 1)), {k, 1, Infinity}], 10, 120][[1]]
%Y A308642 Cf. A005448, A084248, A308666.
%K A308642 nonn,cons,changed
%O A308642 1,1
%A A308642 _Ilya Gutkovskiy_, Jun 15 2019