A031513 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 15.

227, 239, 243, 251, 263, 267, 271, 283, 287, 904, 928, 1000, 1096, 1120, 1152, 2031, 2103, 2175, 2235, 2247, 2319, 2391, 2463, 2523, 2595, 3608, 3672, 3736, 3928, 3992, 4184, 4232, 4248, 4376, 4504, 4568, 4616, 5635, 5735, 5815, 5935, 6015, 6115, 6135

Offset

1,1

Links

Table of n, a(n) for n=1..44.

Mathematica

epct15Q[n_]:=Module[{s=Sqrt[n], cf}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; EvenQ[Length[cf]]&&cf[[Length[cf]/2]] ==15]; Select[Range[6200], epct15Q] (* Harvey P. Dale, May 30 2013 *)

Crossrefs

Sequence in context: A050847 A098247 A092994 * A078765 A179141 A259059

Adjacent sequences: A031510 A031511 A031512 * A031514 A031515 A031516

Keyword

nonn

Author

David W. Wilson

Status

approved