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.

82, 2141, 4274, 6970, 7306, 10525, 10937, 14569, 15053, 18994, 20389, 24314, 25253, 25889, 30637, 31337, 36541, 43793, 47618, 51701, 52154, 52609, 53066, 54449, 55381, 62233, 70537, 71597, 72665, 80485, 81050, 82757, 83905, 85061, 85642, 86225, 86810

Offset

1,1

Links

Table of n, a(n) for n=1..37.

Mathematica

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 *)

Crossrefs

Subsequence of A003814.

Sequence in context: A280857 A281603 A234253 * A232904 A230395 A017798

Adjacent sequences: A031603 A031604 A031605 * A031607 A031608 A031609

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected by Harvey P. Dale, Nov 12 2013

Status

approved