login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A031601 Numbers n such that continued fraction for sqrt(n) has odd period and central terms 13. 1
409, 1181, 2258, 3562, 3802, 3925, 5305, 5897, 8269, 9829, 10834, 11041, 12389, 15737, 16745, 17785, 21757, 23029, 23633, 24554, 25178, 26869, 27194, 27521, 28181, 28514, 28849, 30554, 30901, 32413, 33853, 36073, 36185, 40841, 41362, 41765, 42170 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..150

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]] (* Harvey P. Dale, Nov 23 2011 *)

CROSSREFS

Sequence in context: A321151 A052376 A201483 * A107625 A061333 A262636

Adjacent sequences:  A031598 A031599 A031600 * A031602 A031603 A031604

KEYWORD

nonn

AUTHOR

David W. Wilson

EXTENSIONS

Corrected by Harvey P. Dale, Nov 23 2011

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 March 18 16:00 EDT 2019. Contains 321292 sequences. (Running on oeis4.)