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 A013650 #18 Aug 09 2025 04:58:08 %S A013650 7,32,75,88,136,215,279,280,312,403,427,560,711,736,851,880,923,1007, %T A013650 1067,1272,1311,1363,1431,1495,1736,1855,1887,1955,1976,1995,2128, %U A013650 2159,2184,2272,2511,2567,2640,2728,2880,3055,3211,3560,3751,3811,3927,3984 %N A013650 Numbers k such that the period of the continued fraction for sqrt(k) contains exactly three 1's. %D A013650 Kenneth H. Rosen, Elementary Number Theory and Its Applications, Addison-Wesley, 1984, p. 426 (but beware of errors!). %H A013650 Amiram Eldar, <a href="/A013650/b013650.txt">Table of n, a(n) for n = 1..10000</a> %t A013650 Select[ Range@ 1900, !IntegerQ[ Sqrt@ #] && Count[ ContinuedFraction[ Sqrt@ #][[2]], 1] == 3 &] (* _Robert G. Wilson v_, Jul 03 2011 *) %K A013650 nonn %O A013650 1,1 %A A013650 _Clark Kimberling_