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 A279424 #6 Jun 05 2017 18:14:27 %S A279424 2,12,21,29,102,107,116,120,132,136,143,153,180,183,191,196,201,206, %T A279424 220,229,271,280,294,299,304,309,1002,1007,1012,1017,1022,1027,1046, %U A279424 1051,1065,1070,1079,1093,1102,1111,1120,1129,1142,1151,1155,1164,1168,1181 %N A279424 Numbers k such that k^2 has an odd number of digits and the middle digit is 4. %H A279424 Lars Blomberg, <a href="/A279424/b279424.txt">Table of n, a(n) for n = 1..10000</a> %e A279424 2^2 = (4), 136^2 = 18(4)96, 1017^2 = 103(4)289. %t A279424 Select[Range[1200],OddQ[IntegerLength[#^2]]&&IntegerDigits[#^2][[(IntegerLength[ #^2]+1)/2]]==4&] (* _Harvey P. Dale_, Jun 05 2017 *) %Y A279424 Cf. A279420-A279423, A279425-A279429. %K A279424 nonn,base,easy %O A279424 1,1 %A A279424 _Lars Blomberg_, Dec 22 2016