A031615 Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 27.

4649, 9458, 15457, 15706, 22621, 31853, 32569, 41434, 53189, 54113, 56458, 66925, 67961, 81097, 82237, 99754, 101653, 102929, 114869, 115546, 116906, 118274, 121034, 121729, 122426, 137629, 154505, 160841, 162445, 164057, 175685, 176522, 178202, 179890

Offset

1,1

Links

Table of n, a(n) for n=1..34.

Mathematica

cf27Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {0, 0}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len] && cf[[(len+1)/2]]==27]; Select[Range[200000], cf27Q] (* Harvey P. Dale, Mar 27 2015 *)

Crossrefs

Sequence in context: A068268 A227482 A028551 * A122713 A235235 A118815

Adjacent sequences: A031612 A031613 A031614 * A031616 A031617 A031618

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected and extended by Harvey P. Dale, Mar 27 2015

Status

approved