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!)
A031631 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 43. 0
11689, 23458, 37717, 38890, 56765, 78569, 79693, 106501, 138673, 139418, 171757, 204745, 210205, 212041, 248533, 252533, 255554, 290069, 291146, 293306, 294389, 295474, 296561, 298741, 299834, 300929, 302026, 395225, 402797, 405337 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..30.

MATHEMATICA

cf43Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 43]; Select[Range[406000], cf43Q] (* Harvey P. Dale, Aug 25 2019 *)

CROSSREFS

Sequence in context: A254770 A254777 A254723 * A250923 A015630 A237933

Adjacent sequences:  A031628 A031629 A031630 * A031632 A031633 A031634

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

First term 1850 removed by Georg Fischer, Jun 16 2019

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 22 17:42 EDT 2022. Contains 353957 sequences. (Running on oeis4.)