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A031603 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 15. 0

%I #14 Aug 18 2021 00:10:32

%S 2858,3074,5122,7177,7517,9773,10169,13681,14149,16673,17189,17713,

%T 17978,18514,20525,21097,22265,22861,26041,27337,27997,30113,32213,

%U 33653,35594,35969,37489,37874,38261,39041,39434,39829,45673,52825,54785,55717

%N 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 15.

%t opct15Q[n_]:=Module[{sr=Sqrt[n],cf,len},cf=If[IntegerQ[sr],{}, ContinuedFraction[ sr][[2]]];len=Length[cf];OddQ[len]&&Take[cf,{Floor[ len/2],Floor[len/2]+1}]=={15,15}]; Select[Range[56000],opct15Q] (* _Harvey P. Dale_, Jun 11 2013 *)

%Y Subsequence of A003814.

%K nonn

%O 1,1

%A _David W. Wilson_

%E Corrected by _Harvey P. Dale_, Jun 11 2013

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Last modified July 13 11:10 EDT 2024. Contains 374282 sequences. (Running on oeis4.)