A031666 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 78.

13933, 123985, 124690, 126106, 185021, 258233, 260269, 262313, 347146, 550925, 553897, 559865, 679417, 823178, 953201, 957109, 959066, 962986, 964949, 966914, 972821, 974794, 1120093, 1286797, 1295885, 1467482, 1474757, 1477186

Offset

1,1

Links

Table of n, a(n) for n=1..28.

Mathematica

cf78Q[n_]:=Module[{s=Sqrt[n], len, cf}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[s][[2]]]; len= Length[ cf]; OddQ[len]&&cf[[Floor[len/2]]]==cf[[Ceiling[len/2]]]==78]; Select[Range[ 1480000], cf78Q] (* Harvey P. Dale, Dec 16 2023 *)

Crossrefs

Subsequence of A003814.

Sequence in context: A237571 A244273 A118464 * A031819 A066939 A215150

Adjacent sequences: A031663 A031664 A031665 * A031667 A031668 A031669

Keyword

nonn

Author

David W. Wilson

Extensions

First term 6085 removed by Georg Fischer, Jun 16 2019

Status

approved