A031679 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 91.

52009, 169825, 170650, 252125, 350633, 466714, 474946, 600914, 604018, 605573, 757261, 760745, 914377, 925885, 929737, 1098833, 1103029, 1109338, 1113554, 1117778, 1297946, 1302506, 1304789, 1313941, 1316234, 1318529, 1320826

Offset

1,1

Links

Table of n, a(n) for n=1..27.

Mathematica

cf91Q[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]] == 91]; Select[Range[14*10^5], cf91Q] (* Harvey P. Dale, Sep 23 2018 *)

Crossrefs

Sequence in context: A253996 A258906 A234181 * A234679 A191303 A291869

Adjacent sequences: A031676 A031677 A031678 * A031680 A031681 A031682

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected by Harvey P. Dale, Sep 23 2018

Status

approved