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 A279423 #6 Apr 06 2018 14:32:18
%S A279423 111,124,128,139,146,156,177,188,213,231,269,287,312,1036,1041,1055,
%T A279423 1060,1074,1088,1097,1106,1115,1124,1133,1146,1159,1172,1189,1193,
%U A279423 1214,1218,1222,1226,1274,1278,1282,1286,1305,1309,1313,1328,1343,1354,1365,1376
%N A279423 Numbers k such that k^2 has an odd number of digits and the middle digit is 3.
%H A279423 Lars Blomberg, <a href="/A279423/b279423.txt">Table of n, a(n) for n = 1..10000</a>
%e A279423 111^2 = 12(3)21, 231^2 = 53(3)61, 1214^2 = 147(3)796.
%t A279423 ond3Q[n_]:=Module[{idn2=IntegerDigits[n^2],len},len=Length[idn2];OddQ[ len] && idn2[[(len+1)/2]]==3]; Select[Range[1400],ond3Q] (* _Harvey P. Dale_, Apr 06 2018 *)
%Y A279423 Cf. A279420-A279422, A279424-A279429.
%K A279423 nonn,base,easy
%O A279423 1,1
%A A279423 _Lars Blomberg_, Dec 22 2016