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 A010333 #21 Jan 22 2018 16:00:57 %S A010333 1,1,1,5,1,1,5,1,3,1,5,7,11,1,7,5,1,5,5,11,1,9,15,9,1,5,3,9,1,9,17,1, %T A010333 5,21,5,13,1,7,5,1,5,11,17,7,1,9,3,7,21,13,1,5,11,17,7,11,1,19,5,5,7, %U A010333 15,1,5,3,5,9,21,21,1,21,37,7,21,1,5,17,25,3,15,13,1,9,19,19,1,5,7,39 %N A010333 Length of period of continued for sqrt(A003814(n)). %C A010333 If the period length of the continued fraction of a quadratic surd sqrt(D) is odd, the negative Pell equation x^2 - D y^2 = -1 has (infinite) solutions. %H A010333 Ray Chandler, <a href="/A010333/b010333.txt">Table of n, a(n) for n = 1..10000</a> %t A010333 Select[Map[Length@ Last@ ContinuedFraction@ Sqrt@ # &, Range[550]], OddQ] (* _Michael De Vlieger_, Dec 06 2017, after _T. D. Noe_ at A003814 *) %Y A010333 Cf. A003814. %K A010333 nonn %O A010333 1,4 %A A010333 _N. J. A. Sloane_, Walter Gilbert