%N Length of period of continued for sqrt(A003814(n)).
%C 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 Ray Chandler, <a href="/A010333/b010333.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Map[Length@ Last@ ContinuedFraction@ Sqrt@ # &, Range], OddQ] (* _Michael De Vlieger_, Dec 06 2017, after _T. D. Noe_ at A003814 *)
%Y Cf. A003814.
%A _N. J. A. Sloane_, Walter Gilbert