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 A343201 #8 Jul 08 2021 02:48:59
%S A343201 3,7,2,1,3,8,4,4,1,6,3,2,0,4,2,8,1,4,6,8,1,9,9,1,9,4,1,5,8,5,5,8,3,9,
%T A343201 6,9,0,2,0,7,3,7,9,4,5,6,3,9,7,7,3,2,7,9,5,2,1,9,7,2,3,0,7,5,5,8,8,7,
%U A343201 8,3,4,2,7,7,7,1,3,1,5,5,1,1,0,8,9,1,0
%N A343201 Decimal expansion of Sum_{n>=1} (-1)^(n+1)*K(n)/n!, where K(n) is the Kempner function (A002034).
%C A343201 This constant is irrational (Sàndor, 1997).
%H A343201 József Sàndor, <a href="https://doi.org/10.5281/ZENODO.8868">On the irrationality of certain alternative Smarandache series</a>, in: C. Dumitrescu and V. Seleacu (eds.), Proceedings of the first international conference on Smarandache type notions in number theory, University of Craiova, 21-24 August 1997, American Research Press, 1997, pp. 124-125.
%e A343201 0.37213844163204281468199194158558396902073794563977...
%t A343201 kempner[n_] := Module[{k = 1}, While[! Divisible[k!, n], k++]; k]; RealDigits[Sum[(-1)^(n + 1) * kempner[n]/n!, {n, 1, 100}], 10, 100][[1]]
%Y A343201 Cf. A002034, A048834.
%K A343201 nonn,cons
%O A343201 0,1
%A A343201 _Amiram Eldar_, Jul 07 2021