A031631 - OEIS

A031631

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 43.

11689, 23458, 37717, 38890, 56765, 78569, 79693, 106501, 138673, 139418, 171757, 204745, 210205, 212041, 248533, 252533, 255554, 290069, 291146, 293306, 294389, 295474, 296561, 298741, 299834, 300929, 302026, 395225, 402797, 405337

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..30.

MATHEMATICA

cf43Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 43]; Select[Range[406000], cf43Q] (* Harvey P. Dale, Aug 25 2019 *)

CROSSREFS

Sequence in context: A254777 A254723 A354212 * A250923 A015630 A237933

Adjacent sequences: A031628 A031629 A031630 * A031632 A031633 A031634

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

First term 1850 removed by Georg Fischer, Jun 16 2019

STATUS

approved