A031575 - OEIS

A031575

Numbers k such 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.

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

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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