A031510 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 12.

146, 158, 162, 166, 178, 194, 327, 366, 372, 381, 393, 417, 429, 438, 580, 596, 604, 628, 636, 652, 668, 684, 692, 700, 716, 724, 740, 748, 764, 772, 780, 905, 945, 955, 995, 1005, 1030, 1055, 1070, 1195, 1205, 1220, 1302, 1338, 1434, 1578, 1614, 1626, 1758

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

epct12Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 12]; Select[Range[2000], epct12Q] (* Harvey P. Dale, Jan 04 2015 *)

Crossrefs

Sequence in context: A166071 A124969 A294594 * A145915 A248406 A135666

Adjacent sequences: A031507 A031508 A031509 * A031511 A031512 A031513

Keyword

nonn

Author

David W. Wilson

Status

approved