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A031606 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 18. 0

%I #15 Aug 18 2021 00:10:32

%S 82,2141,4274,6970,7306,10525,10937,14569,15053,18994,20389,24314,

%T 25253,25889,30637,31337,36541,43793,47618,51701,52154,52609,53066,

%U 54449,55381,62233,70537,71597,72665,80485,81050,82757,83905,85061,85642,86225,86810

%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 18.

%t opct18Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{0,0},ContinuedFraction[s][[2]]];len=Length[cf];OddQ[len] && cf[[(len+1)/2]] == 18]; Select[Range[90000],opct18Q] (* _Harvey P. Dale_, Nov 12 2013 *)

%Y Subsequence of A003814.

%K nonn

%O 1,1

%A _David W. Wilson_

%E Corrected by _Harvey P. Dale_, Nov 12 2013

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Last modified June 15 19:43 EDT 2024. Contains 373410 sequences. (Running on oeis4.)