A031672 - OEIS

A031672

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 84.

1765, 143722, 144481, 215417, 405994, 511514, 514378, 515813, 518689, 781897, 796105, 941429, 947258, 951154, 1105226, 1122106, 1126346, 1304893, 1494125, 1499017, 1508825, 1513741, 1711825, 1714442, 1730186, 1732817, 1927633, 1933189, 1941538

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..29.

MATHEMATICA

cf84Q[n_]:=Module[{s=Sqrt[n], c, len}, c=If[IntegerQ[s], {0, 0}, ContinuedFraction[ s][[2]]]; len=Length[c]; OddQ[len]&&c[[(len+1)/2]] == 84]; Select[Range[2*10^6], cf84Q] (* Harvey P. Dale, Jul 31 2016 *)

CROSSREFS

Sequence in context: A343989 A343988 A031762 * A031540 A135795 A206201

Adjacent sequences: A031669 A031670 A031671 * A031673 A031674 A031675

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

Corrected and extended by Harvey P. Dale, Jul 31 2016

STATUS

approved