A031559 that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 61.

3723, 3727, 3739, 3767, 3779, 3791, 3803, 3823, 3827, 3847, 3851, 3859, 3863, 3867, 3871, 3907, 3911, 3919, 3923, 3931, 3943, 3947, 3967, 14888, 14920, 14944, 14976, 15016, 15040, 15072, 15080, 15104, 15168, 15200, 15208, 15232, 15264, 15360, 15392

Offset

1,1

Links

Table of n, a(n) for n=1..39.

Mathematica

cf61Q[n_]:=Module[{srt=Sqrt[n], len, cf}, cf=ContinuedFraction[srt]; If[ IntegerQ[srt], len=1, len=Length[cf[[2]]]]; EvenQ[len]&&cf[[2]][[len/2]]==61]; Select[Range[15400], cf61Q] (* Harvey P. Dale, Jun 12 2012 *)

Crossrefs

Sequence in context: A260860 A221013 A224436 * A031739 A251206 A038012

Adjacent sequences: A031556 A031557 A031558 * A031560 A031561 A031562

Keyword

nonn

Author

David W. Wilson

Status

approved