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A010333 Length of period of continued for sqrt(A003814(n)). 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

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

MATHEMATICA

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

CROSSREFS

Cf. A003814.

Sequence in context: A071170 A332762 A108691 * A131777 A323388 A260877

Adjacent sequences:  A010330 A010331 A010332 * A010334 A010335 A010336

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Walter Gilbert

STATUS

approved

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Last modified September 17 06:16 EDT 2021. Contains 347478 sequences. (Running on oeis4.)