login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A031511 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 13. 0
171, 179, 187, 191, 199, 211, 223, 680, 704, 768, 800, 808, 832, 864, 872, 896, 1527, 1587, 1671, 1815, 1875, 1959, 2019, 2712, 2776, 2824, 3032, 3208, 3288, 3352, 3464, 3544, 3592, 4235, 4315, 4415, 4435, 4535, 4615, 4735, 4815, 4835, 4915, 5035, 5135 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..45.

MATHEMATICA

ct13Q[n_]:=Module[{s=Sqrt[n], cf}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; EvenQ[Length[cf]]&&cf[[(Length[cf])/2]] == 13]; Select[Range[5200], ct13Q] (* Harvey P. Dale, Sep 04 2018 *)

CROSSREFS

Sequence in context: A187140 A185845 A045149 * A101273 A136365 A031900

Adjacent sequences:  A031508 A031509 A031510 * A031512 A031513 A031514

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 22 23:50 EST 2022. Contains 350504 sequences. (Running on oeis4.)