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 A031630 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 42. 0
 11261, 21953, 22549, 36181, 36562, 37330, 53945, 54877, 55817, 132058, 165197, 166825, 199357, 235754, 238673, 240629, 242593, 243578, 277301, 283649, 284714, 285781, 287921, 337129, 372941, 377837, 426065, 427370, 428677, 431297 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..30. MATHEMATICA cf42Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 2}, ContinuedFraction[s][[2]]]; len= Length[ cf]; OddQ[len]&&cf[[Floor[len/2]]]==cf[[Ceiling[len/2]]]==42]; Select[Range[ 450000], cf42Q] (* Harvey P. Dale, Aug 10 2023 *) CROSSREFS Sequence in context: A104316 A237171 A246248 * A064870 A051520 A051346 Adjacent sequences: A031627 A031628 A031629 * A031631 A031632 A031633 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS First term 1765 removed by Georg Fischer, Jun 16 2019 STATUS approved

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Last modified May 29 00:29 EDT 2024. Contains 372921 sequences. (Running on oeis4.)