Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #17 Dec 04 2024 23:07:47
%S 15,21,34,47,58,67,88,94,105,106,107,108,109,149,150,151,182,183,184,
%T 210,211,212,235,236,257,258,278,279,297,298,315,316,332,333,334,335,
%U 336,337,338,339,340,341,342,343,344,345,346,470,471,472,473,474,475,476
%N Numbers whose square starts with 2 identical digits.
%H Alois P. Heinz, <a href="/A123912/b123912.txt">Table of n, a(n) for n = 1..10000</a>
%e 15^2 = 225.
%p q:= n-> (s-> is(s[1]=s[2]))(""||(n^2)):
%p select(q, [$4..1000])[]; # _Alois P. Heinz_, Apr 22 2022
%t 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 (PARI) isok(k) = my(d=digits(k^2)); (#d>=2) && (d[1]==d[2]); \\ _Michel Marcus_, Nov 27 2024
%K base,nonn
%O 1,1
%A _Tanya Khovanova_, Oct 28 2006