A031407 Numbers k such that the continued fraction for sqrt(k) has even period 2*m and the m-th term of the periodic part is 4.

18, 22, 34, 39, 57, 68, 69, 76, 78, 92, 105, 108, 116, 124, 140, 150, 155, 174, 186, 203, 205, 217, 220, 259, 264, 266, 282, 294, 301, 308, 318, 329, 333, 369, 371, 376, 378, 406, 410, 413, 423, 434, 450, 456, 477, 490, 495, 504, 517, 522, 549, 550, 558

Offset

1,1

Links

T. D. Noe, Table of n, a(n) for n = 1..1000

Mathematica

n = 1; t = {}; While[Length[t] < 50, n++; If[! IntegerQ[Sqrt[n]], c = ContinuedFraction[Sqrt[n]]; len = Length[c[[2]]]; If[EvenQ[len] && c[[2, len/2]] == 4, AppendTo[t, n]]]]; t (* T. D. Noe, Apr 04 2014 *)

Crossrefs

Cf. A031404-A031423.

Sequence in context: A096282 A250737 A290172 * A267826 A339473 A361627

Adjacent sequences: A031404 A031405 A031406 * A031408 A031409 A031410

Keyword

nonn

Author

David W. Wilson

Status

approved