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A031573 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 75. 0
5627, 5639, 5643, 5647, 5651, 5659, 5667, 5683, 5711, 5723, 5731, 5739, 5743, 5763, 5767, 5779, 5783, 5787, 5791, 5807, 5827, 5831, 5839, 5843, 5851, 5867, 5879, 5891, 5899, 5903, 5923, 5927, 22504, 22528, 22624, 22656, 22688, 22696, 22720, 22784 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The "central term" is at period/2, not at period/2 + 1. - Harvey P. Dale, Feb 20 2013

LINKS

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

MATHEMATICA

epQ[n_]:=Module[{srt=Sqrt[n], cf, len}, cf=If[IntegerQ[srt], {1}, ContinuedFraction[ srt] [[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]]==75]; Select[Range[ 23000], epQ] (* Harvey P. Dale, Feb 20 2013 *)

CROSSREFS

Sequence in context: A247261 A203831 A014799 * A031753 A045128 A229591

Adjacent sequences:  A031570 A031571 A031572 * A031574 A031575 A031576

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified September 25 17:17 EDT 2022. Contains 356986 sequences. (Running on oeis4.)