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 A279427 #7 Oct 03 2023 20:04:41 %S A279427 24,26,113,137,144,154,181,189,214,223,234,266,277,286,311,1033,1038, %T A279427 1043,1057,1062,1071,1076,1085,1099,1108,1117,1126,1139,1148,1152, %U A279427 1161,1165,1178,1182,1199,1203,1228,1232,1236,1240,1244,1248,1252,1256,1260,1264 %N A279427 Numbers k such that k^2 has an odd number of digits and the middle digit is 7. %H A279427 Lars Blomberg, <a href="/A279427/b279427.txt">Table of n, a(n) for n = 1..10000</a> %e A279427 24^2 = 5(7)6, 223^2 = 49(7)29, 1152^2 = 132(7)104. %t A279427 Select[Range[1264], OddQ[len=Length[IntegerDigits[#^2]]]&&Part[IntegerDigits[#^2], (len+1)/2]==7 &] (* _Stefano Spezia_, Oct 03 2023 *) %Y A279427 Cf. A279420-A279426, A279428-A279429. %K A279427 nonn,base,easy %O A279427 1,1 %A A279427 _Lars Blomberg_, Dec 22 2016