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 A113800 #15 Jul 22 2021 07:53:01
%S A113800 2,231,1010,102010,451429,1000100,9426681,1000001000,8803095102,
%T A113800 10002000100,56017891104,1000000010000,4811618419542
%N A113800 Numbers k such that k^2 plus the reverse of k^2 gives a perfect power.
%C A113800 Sequence is infinite since it contains all the numbers of the form (1+100^k)*10^k and (1+100^k)^2*10^k, for k >= 1. - _Giovanni Resta_, Sep 24 2013
%e A113800 451429^2 = 203788142041 and 203788142041 + 140241887302 = 7007^3,
%e A113800 9426681^2 = 88862314675761 and 88862314675761 + 16757641326888 = 10277157^2.
%t A113800 ppQ[n_] := n != 1 && GCD @@ (Transpose[FactorInteger[n]][[2]]) > 1; rev[n_] := FromDigits@Reverse@IntegerDigits@n ; lst = {}; Do[If[ppQ[n^2 + rev[n^2]], AppendTo[lst, n]], {n, 10^6}]; lst
%Y A113800 Cf. A000290, A002942, A061226.
%K A113800 base,nonn,more
%O A113800 1,1
%A A113800 _Giovanni Resta_, Jan 22 2006
%E A113800 a(8)-a(13) from _Giovanni Resta_, Sep 24 2013