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 A113621 #18 Jul 22 2021 07:51:38
%S A113621 1,20,29,170,176,241,3136,9800,20309,20486,53663,73793,94836,200000
%N A113621 Numbers k such that the representation of k^2 is a substring of that of k!, in base 10.
%C A113621 Using one of the fast algorithms for computing the last nonzero digit of the factorial (A008904) it is easy to see that also 200000000 and 2*10^16 are terms.
%e A113621 29^2 = 841 and 29! = 8(841)761993739701954543616000000.
%t A113621 lst={}; Do[If[{}!= StringPosition[ToString[n! ], ToString[n^2]], AppendTo[lst, n]], {n, 10000}]; lst
%Y A113621 Cf. A033180, A008904.
%Y A113621 CF. A000142, A000290.
%K A113621 base,nonn,more
%O A113621 1,2
%A A113621 _Giovanni Resta_, Jan 26 2006
%E A113621 Extended by _Giovanni Resta_, Apr 04 2014