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 A279426 #6 May 28 2023 15:01:32 %S A279426 13,19,31,103,108,117,121,125,129,133,140,147,157,160,175,178,194,199, %T A279426 204,209,216,225,236,238,240,260,262,264,275,284,291,296,301,306,1003, %U A279426 1008,1013,1018,1023,1028,1047,1052,1066,1080,1094,1103,1112,1121,1130 %N A279426 Numbers k such that k^2 has an odd number of digits and the middle digit is 6. %H A279426 Lars Blomberg, <a href="/A279426/b279426.txt">Table of n, a(n) for n = 1..10000</a> %e A279426 13^2 = 1(6)9, 133^2 = 17(6)89, 284^2 = 80(6)56. %t A279426 Select[Range[1200],OddQ[IntegerLength[#^2]]&&IntegerDigits[#^2][[(IntegerLength[ #^2]+1)/2]] == 6&] (* _Harvey P. Dale_, May 28 2023 *) %Y A279426 Cf. A279420-A279425, A279427-A279429. %K A279426 nonn,base,easy %O A279426 1,1 %A A279426 _Lars Blomberg_, Dec 22 2016