The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A031601 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A031601

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 13.
(history; published version)

#24 by N. J. A. Sloane at Wed Aug 18 00:10:32 EDT 2021

NAME

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 13.

Discussion

Wed Aug 18

00:10

OEIS Server: https://oeis.org/edit/global/2908

#23 by Alois P. Heinz at Sun Jul 11 08:56:44 EDT 2021

STATUS

proposed

approved

#22 by Michel Marcus at Sun Jul 11 08:52:12 EDT 2021

STATUS

editing

proposed

#21 by Michel Marcus at Sun Jul 11 08:52:09 EDT 2021

CROSSREFS

Subsequence of A003814.

STATUS

proposed

editing

#20 by Jon E. Schoenfield at Sun Jul 11 08:24:32 EDT 2021

STATUS

editing

proposed

#19 by Jon E. Schoenfield at Sun Jul 11 08:24:31 EDT 2021

NAME

Numbers n k such that the continued fraction for sqrt(nk) has odd period and central terms 13.

STATUS

approved

editing

#18 by Alois P. Heinz at Thu Oct 31 17:45:58 EDT 2013

STATUS

editing

approved

#17 by Alois P. Heinz at Thu Oct 31 17:45:53 EDT 2013

MATHEMATICA

cf13Q[n_]:=Module[{per=ContinuedFraction[Sqrt[n]][[2]]}, OddQ[Length[ per]]&&per[[Floor[Length[per]/2]+1]]==13]; nn=43000; With[{terms = Complement[Range[nn], Range[Floor[Sqrt[nn]]]^2]}, Select[terms, cf13Q]] (* From _Harvey P. Dale, _, Nov 23 2011 *)

EXTENSIONS

Corrected by _Harvey P. Dale, _, Nov 23 2011

STATUS

approved

editing

#16 by Russ Cox at Fri Mar 30 18:35:29 EDT 2012

AUTHOR

_David W. Wilson (davidwwilson(AT)comcast.net)_

Discussion

Fri Mar 30

18:35

OEIS Server: https://oeis.org/edit/global/202

#15 by Joerg Arndt at Mon Feb 13 06:47:20 EST 2012

STATUS

proposed

approved