A031419 - OEIS

A031419

Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted then there are a pair of central terms both equal to 6.

109, 281, 865, 922, 1277, 1613, 1769, 1933, 2161, 2341, 2789, 3098, 3653, 3961, 4285, 4457, 5065, 5153, 5713, 5858, 5954, 6101, 6458, 6554, 6709, 7129, 7349, 7681, 8237, 8941, 9242, 9305, 9677, 10177, 10498, 10565, 10693, 10762, 11162, 11365, 11698

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000 [shifted by Georg Fischer, Jun 23 2019]

MATHEMATICA

n = 1; t = {}; While[Length[t] < 50, n++; If[! IntegerQ[Sqrt[n]], c = ContinuedFraction[Sqrt[n]]; len = Length[c[[2]]]; If[OddQ[len] && c[[2, (len + 1)/2]] == 6 && c[[2, (len + 1)/2 - 1]] == 6, AppendTo[t, n]]]]; t (* T. D. Noe, Apr 04 2014; corrected by Georg Fischer, Jun 23 2019 *)

CROSSREFS

Cf. A031404-A031423.

Subsequence of A003814.

Sequence in context: A193397 A193395 A140036 * A183349 A238682 A070180

Adjacent sequences: A031416 A031417 A031418 * A031420 A031421 A031422

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

a(1) corrected by T. D. Noe, Apr 04 2014

a(1) = 10 removed by Georg Fischer, Jun 23 2019

STATUS

approved