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 A347352 #10 Feb 16 2025 08:34:02
%S A347352 7,5,9,2,2,3,1,0,1,8,5,1,6,0,3,7,7,9,5,7,7,7,5,9,0,4,4,9,5,5,8,4,5,5,
%T A347352 9,5,9,1,3,3,5,2,4,0,2,1,8,4,4,8,1,9,8,3,6,0,9,5,2,0,8,1,4,5,5,5,0,3,
%U A347352 7,8,6,2,2,8,6,4,0,9,4,5,3,7,4,7,6,6,7,6,9,7,6,7,3,9,5,3,9,8,2,7,7,7,6,5,6,1,4,7,4,1,8,8,0,8,5
%N A347352 Decimal expansion of 1 / 1^1 - 1 / (1^1 * 2^2) + 1 / (1^1 * 2^2 * 3^3) - 1 / (1^1 * 2^2 * 3^3 * 4^4) + ...
%H A347352 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Hyperfactorial.html">Hyperfactorial</a>.
%e A347352 0.759223101851603779577759044955845595913352402184...
%t A347352 With[{m = 105}, RealDigits[N[Sum[(-1)^(n + 1)/Hyperfactorial[n], {n, 1, Infinity}], m + 2], 10, m][[1]]] (* _Amiram Eldar_, Apr 30 2023 *)
%Y A347352 Cf. A000312, A002109, A068996, A073009, A083648, A137986, A287013, A347345.
%K A347352 nonn,cons
%O A347352 0,1
%A A347352 _Ilya Gutkovskiy_, Aug 28 2021