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A010333 Length of period of continued for sqrt(A003814(n)). 2


%S 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 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 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 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[550]], OddQ] (* _Michael De Vlieger_, Dec 06 2017, after _T. D. Noe_ at A003814 *)

%Y Cf. A003814.

%K nonn

%O 1,4

%A _N. J. A. Sloane_, Walter Gilbert

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Last modified October 23 11:14 EDT 2021. Contains 348211 sequences. (Running on oeis4.)