OFFSET
1,1
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1664
FORMULA
G.f.: Sum_{k>=1} C(2k, k)*x^k/(1-x^k). - Benoit Cloitre, Apr 21 2003
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(binomial(2*k,k)/k)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, May 20 2018
a(n) ~ 4^n / sqrt(Pi*n). - Vaclav Kotesovec, May 21 2018
a(n) = Sum_{k=1..n} C(2*gcd(n,k),gcd(n,k))/phi(n/gcd(n,k)) = Sum_{k=1..n} C(2*n/gcd(n,k),n/gcd(n,k))/phi(n/gcd(n,k)) where phi = A000010. - Richard L. Ollerton, May 19 2021
MATHEMATICA
Table[Total[Binomial[2#, #]&/@Divisors[n]], {n, 30}] (* Harvey P. Dale, Aug 20 2022 *)
PROG
(PARI) a(n)=sumdiv(n, d, binomial(2*d, d))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Aug 13 2002
STATUS
approved