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 A363842 #12 Jun 25 2023 08:13:17
%S A363842 2,2,5,0,0,0,1,9,2,9,0,1,2,3,4,5,6,7,9,0,1,2,3,4,5,6,7,9,0,1,2,3,4,5,
%T A363842 6,7,9,0,1,2,3,4,5,6,7,9,0,1,4,9,4,3,3,7,7,0,1,0,4,2,8,4,9,4,1,6,2,2,
%U A363842 0,3,5,2,4,4,3,4,4,8,0,7,7,5,8,5,2,2,5
%N A363842 Decimal expansion of Sum_{k>=0} 1/(k!)!^2.
%C A363842 1166401/518400 approximates this constant to 48 significant digits.
%e A363842 2.25000192901234567901234567901234567901234567901...
%t A363842 RealDigits[Sum[1/(k!)!^2, {k, 0, 4}], 10, 100][[1]]
%o A363842 (PARI) suminf(k=0, 1/k!!^2)
%Y A363842 Cf. A363841 (continued fraction).
%Y A363842 Cf. A336686.
%K A363842 nonn,cons
%O A363842 1,1
%A A363842 _Daniel Hoyt_, Jun 23 2023