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 A020440 #16 Aug 09 2025 04:58:23 %S A020440 13,21,31,57,61,67,73,74,92,106,108,109,111,112,116,129,137,158,161, %T A020440 162,183,185,193,204,207,236,237,243,246,251,261,262,265,273,274,275, %U A020440 282,297,298,308,314,317,329,332,341,346,351,355,364,375,381,383,384,388,406,412 %N A020440 Numbers k such that the period of the continued fraction for sqrt(k) contains exactly four 1's. %H A020440 Amiram Eldar, <a href="/A020440/b020440.txt">Table of n, a(n) for n = 1..10000</a> %t A020440 Select[ Range@ 1900, !IntegerQ[ Sqrt@ #] && Count[ ContinuedFraction[ Sqrt@ #][[2]], 1] == 4 &] (* _Robert G. Wilson v_, Jul 03 2011 *) %K A020440 nonn %O A020440 1,1 %A A020440 _David W. Wilson_