A081768 Number of k, 1<=k<=n, such that C(n,k) divides C(2n,2k).

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

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