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A031575 that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 77. 0
5931, 5939, 5987, 5999, 6007, 6011, 6043, 6047, 6059, 6067, 6079, 6091, 6103, 6131, 6143, 6151, 6163, 6167, 6171, 6191, 6199, 6203, 6211, 6219, 6223, 6239, 23720, 23808, 23816, 23840, 23872, 23904, 23936, 24008, 24040, 24064, 24128, 24192, 24224, 24256 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..40.

MATHEMATICA

cf77Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len] && cf[[len/2]] == 77]; Select[Range[25000], cf77Q] (* Harvey P. Dale, Oct 13 2015 *)

CROSSREFS

Sequence in context: A252289 A284980 A251464 * A031755 A133598 A028517

Adjacent sequences:  A031572 A031573 A031574 * A031576 A031577 A031578

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified November 28 04:31 EST 2021. Contains 349400 sequences. (Running on oeis4.)