The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A031575 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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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.
(history; published version)

#16 by N. J. A. Sloane at Sat Jul 06 16:10:09 EDT 2024

STATUS

editing

approved

#15 by N. J. A. Sloane at Sat Jul 06 16:10:06 EDT 2024

NAME

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.

STATUS

approved

editing

#14 by N. J. A. Sloane at Tue Aug 17 23:48:27 EDT 2021

NAME

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.

Discussion

Tue Aug 17

23:48

OEIS Server: https://oeis.org/edit/global/2907

#13 by Joerg Arndt at Fri Jul 09 07:25:33 EDT 2021

STATUS

reviewed

approved

#12 by Hugo Pfoertner at Fri Jul 09 05:27:19 EDT 2021

STATUS

proposed

reviewed

#11 by Jon E. Schoenfield at Fri Jul 09 01:42:04 EDT 2021

STATUS

editing

proposed

#10 by Jon E. Schoenfield at Fri Jul 09 01:42:02 EDT 2021

NAME

Numbers n k such that the continued fraction for sqrt(nk) has even period and central term 77.

STATUS

approved

editing

#9 by Harvey P. Dale at Tue Oct 13 15:59:43 EDT 2015

STATUS

editing

approved

#8 by Harvey P. Dale at Tue Oct 13 15:59:37 EDT 2015

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 *)

#7 by Harvey P. Dale at Tue Oct 13 15:59:07 EDT 2015

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 *)

STATUS

approved

editing