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 A134877 #11 Jan 15 2021 09:15:06
%S A134877 1,2,8,7,0,3,7,0,9,6,6,4,1,6,8,1,8,1,4,7,1,1,3,2,0,2,9,7,5,5,8,2,0,4,
%T A134877 2,5,9,0,4,2,1,6,9,5,5,3,4,0,2,2,2,0,8,1,0,2,6,7,9,8,7,6,5,9,2,6,9,0,
%U A134877 9,9,7,3,0,0,3,5,1,8,6,6,5,4,1,9,3,0,7,3,6,8,0,1,0,8,8,0,8,3,9,3,7,7,8,7,5
%N A134877 Decimal expansion of Sum_{k>=1} 1/(k!!)^(k!!).
%e A134877 Sum_{k>=1} 1/(k!!)^(k!!) = 1.28703709664168181471132029755820425904216955340222081026798765926909...
%t A134877 RealDigits[N[Sum[1/n^n, {n, 1, 100}], 200]][[1]]
%Y A134877 Cf. A073009, A100085.
%K A134877 nonn,cons
%O A134877 1,2
%A A134877 _Artur Jasinski_, Nov 14 2007