A031658 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 70.

1226, 61553, 99937, 100570, 101842, 150665, 209933, 276901, 356698, 360289, 362693, 363898, 443917, 446585, 449261, 454637, 651778, 659873, 661498, 664754, 768001, 769754, 771509, 773266, 778549, 780314, 782081, 1037165, 1041241, 1045325, 1049417

Offset

1,1

Links

Table of n, a(n) for n=1..31.

Mathematica

cf70Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 70]; Select[Range[11 10^5], cf70Q] (* Harvey P. Dale, Jul 24 2017 *)

Crossrefs

Sequence in context: A218273 A046177 A031748 * A031533 A031713 A259998

Adjacent sequences: A031655 A031656 A031657 * A031659 A031660 A031661

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected and extended and definition clarified by Harvey P. Dale, Jul 24 2017

Status

approved