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 A123912 #17 Dec 04 2024 23:07:47
%S A123912 15,21,34,47,58,67,88,94,105,106,107,108,109,149,150,151,182,183,184,
%T A123912 210,211,212,235,236,257,258,278,279,297,298,315,316,332,333,334,335,
%U A123912 336,337,338,339,340,341,342,343,344,345,346,470,471,472,473,474,475,476
%N A123912 Numbers whose square starts with 2 identical digits.
%H A123912 Alois P. Heinz, <a href="/A123912/b123912.txt">Table of n, a(n) for n = 1..10000</a>
%e A123912 15^2 = 225.
%p A123912 q:= n-> (s-> is(s[1]=s[2]))(""||(n^2)):
%p A123912 select(q, [$4..1000])[]; # _Alois P. Heinz_, Apr 22 2022
%t A123912 idf[k_]:=IntegerDigits[k^2];Select[Range[4,476],idf[#][[1]]==idf[#][[2]]&] (* Or,to explore member numbers for a range of squares, adjust n2 as needed *) s={};Do[If[IntegerQ[Sqrt[n2]],AppendTo[s,Sqrt[n2]]],{n2,110000,119999}];s (* _James C. McMahon_, Nov 24 2024 *)
%o A123912 (PARI) isok(k) = my(d=digits(k^2)); (#d>=2) && (d[1]==d[2]); \\ _Michel Marcus_, Nov 27 2024
%K A123912 base,nonn
%O A123912 1,1
%A A123912 _Tanya Khovanova_, Oct 28 2006