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

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, 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, 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

Offset: 1

Author

N. J. A. Sloane, Walter Gilbert

Keywords

• nonn

Comments

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.

Links

• Ray Chandler, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003814.

Programs

Mathematica

Select[Map[Length@ Last@ ContinuedFraction@ Sqrt@ # &, Range[550]], OddQ] (* Michael De Vlieger, Dec 06 2017, after T. D. Noe at A003814 *)