A010338 Numbers k such that the continued fraction for sqrt(k) has period 7.

58, 73, 202, 250, 274, 314, 349, 425, 538, 761, 1010, 1073, 1130, 1301, 1546, 1745, 1825, 1898, 2050, 2173, 2258, 2330, 2482, 2581, 2777, 3161, 3202, 3554, 3877, 3890, 4106, 4133, 4346, 4586, 4925, 5162, 5261, 5273, 5297, 5305

Offset: 1

Author

N. J. A. Sloane, Walter Gilbert

Keywords

• nonn

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..10000 (terms n = 1..500 from Harvey P. Dale)

Programs

Mathematica

cfp7Q[n_]:=Module[{s=Sqrt[n]},!IntegerQ[s]&&Length[ ContinuedFraction[ s][[2]]]==7]; Select[Range[6000],cfp7Q] (* Harvey P. Dale, Aug 11 2013 *)

Python

from sympy import continued_fraction_periodic
A010338_list = [n for n, s in ((i, continued_fraction_periodic(0,1,i)[-1]) for i in range(1,10**3)) if isinstance(s, list) and len(s) == 7] # Chai Wah Wu, Jun 08 2017