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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. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 27 14:44 EST 2022. Contains 350607 sequences. (Running on oeis4.)