A031585 that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 87.

7571, 7583, 7587, 7591, 7603, 7607, 7611, 7619, 7639, 7643, 7667, 7679, 7687, 7691, 7699, 7703, 7723, 7727, 7731, 7751, 7759, 7771, 7803, 7811, 7823, 7827, 7831, 7867, 7879, 7883, 7899, 7903, 7907, 7919, 30280, 30304, 30336, 30368, 30376, 30400, 30432

Offset

1,1

Links

Table of n, a(n) for n=1..41.

Mathematica

cf87Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 87]; Select[Range[31000], cf87Q] (* Harvey P. Dale, Jan 24 2019 *)

Crossrefs

Sequence in context: A206173 A205427 A252163 * A031765 A205740 A206672

Adjacent sequences: A031582 A031583 A031584 * A031586 A031587 A031588

Keyword

nonn

Author

David W. Wilson

Status

approved