A031616 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 28.

5209, 16210, 16465, 16981, 24457, 35513, 45169, 46021, 58853, 59338, 60314, 72185, 74345, 75437, 92857, 106154, 107458, 108113, 110753, 123826, 124529, 125941, 127361, 128074, 128789, 131669, 151273, 168941, 170585, 172237, 173897

Offset

1,1

Links

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

Mathematica

cf28Q[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]] == 28]; Rest[Select[Range[174000], cf28Q]] (* Harvey P. Dale, Jun 24 2020 *)

Crossrefs

Subsequence of A003814.

Sequence in context: A109159 A231113 A289514 * A067224 A204139 A237408

Adjacent sequences: A031613 A031614 A031615 * A031617 A031618 A031619

Keyword

nonn

Author

David W. Wilson

Extensions

First term 785 removed by Georg Fischer, Jun 16 2019

Status

approved