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 A031643 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 55. 0
 19069, 38074, 61585, 62581, 63082, 129769, 131213, 173281, 219313, 224018, 225914, 279145, 281261, 407573, 413978, 473969, 478106, 479489, 480874, 482261, 485041, 487829, 489226, 560233, 566233, 650477, 728570, 730277, 733697, 737125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..30. MATHEMATICA ct55Q[n_]:=Module[{c=ContinuedFraction[Sqrt[n]], len}, len=Length[c[[2]]]; OddQ[len]&&Take[c[[2]], {Floor[len/2], Ceiling[len/2]}]=={55, 55}]; cfsqrtn[ upto_]:=Module[{rng=Complement[ Range[upto], Range[Floor[Sqrt[upto]]]^2]}, Select[rng, ct55Q]]; cfsqrtn[740000] (* Harvey P. Dale, Mar 08 2012 *) CROSSREFS Sequence in context: A232576 A339962 A235928 * A261748 A089522 A251041 Adjacent sequences: A031640 A031641 A031642 * A031644 A031645 A031646 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS Corrected by Harvey P. Dale, Mar 08 2012 STATUS approved

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Last modified April 20 03:03 EDT 2024. Contains 371798 sequences. (Running on oeis4.)