login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A081768 Number of k, 1<=k<=n, such that C(n,k) divides C(2n,2k). 1
1, 2, 3, 3, 5, 5, 3, 7, 7, 5, 7, 5, 7, 11, 9, 3, 5, 13, 9, 13, 7, 3, 11, 9, 7, 9, 7, 11, 11, 9, 3, 9, 23, 13, 19, 9, 3, 7, 11, 7, 11, 9, 9, 9, 7, 7, 5, 19, 13, 23, 15, 7, 17, 13, 9, 7, 5, 5, 7, 11, 11, 11, 19, 11, 15, 9, 11, 21, 19, 11, 9, 9, 9, 13, 11, 5, 13, 21, 9, 11, 15, 7, 13, 9, 7, 11, 7, 15 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Is a(n) odd for n>2 ? All odd numbers occur? Does equation a(x)=2m+1 have infinitely many solutions for any m>=1?

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

Total/@Table[If[Divisible[Binomial[2n, 2k], Binomial[n, k]], 1, 0], {n, 90}, {k, n}] (* Harvey P. Dale, Jul 10 2012 *)

CROSSREFS

Sequence in context: A265145 A103310 A046146 * A273493 A193404 A072923

Adjacent sequences:  A081765 A081766 A081767 * A081769 A081770 A081771

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 09 2003

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 April 10 00:05 EDT 2020. Contains 333392 sequences. (Running on oeis4.)