A031628 - OEIS

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A031628

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 40.

401, 10429, 20498, 32842, 33937, 68813, 90826, 92641, 94474, 178525, 180217, 213973, 214898, 216754, 251626, 252629, 253634, 254641, 256661, 257674, 259706, 262769, 344237, 346585, 348941, 353677, 386602, 392837, 396602, 400385, 439333, 443314, 449989

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..33.

MATHEMATICA

op40Q[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]] ==40]; Select[Range[500000], op40Q] (* Harvey P. Dale, Dec 06 2015 *)

CROSSREFS

Subsequence of A003814.

Sequence in context: A031718 A102324 A156785 * A179293 A097742 A115244

Adjacent sequences: A031625 A031626 A031627 * A031629 A031630 A031631

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

Corrected and extended by Harvey P. Dale, Dec 06 2015

STATUS

approved