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 A279421 #6 Jun 06 2018 15:16:52
%S A279421 1,110,119,123,127,131,142,152,182,190,210,224,237,239,261,263,276,
%T A279421 290,310,1035,1040,1059,1073,1087,1096,1105,1123,1132,1141,1145,1154,
%U A279421 1167,1171,1184,1188,1209,1213,1217,1285,1289,1293,1312,1316,1331,1346,1357,1368
%N A279421 Numbers k such that k^2 has an odd number of digits and the middle digit is 1.
%H A279421 Lars Blomberg, <a href="/A279421/b279421.txt">Table of n, a(n) for n = 1..10000</a>
%e A279421 1^2 = (1), 190^2 = 36(1)00, 1145^2 = 131(1)025.
%t A279421 ond1Q[n_]:=Module[{len=IntegerLength[n^2]},OddQ[len]&&IntegerDigits[n^2][[(len+1)/2]]==1]; Select[Range[1500],ond1Q] (* _Harvey P. Dale_, Jun 06 2018 *)
%Y A279421 Cf. A279420, A279422-A279429.
%K A279421 nonn,base,easy
%O A279421 1,2
%A A279421 _Lars Blomberg_, Dec 22 2016