OFFSET
1,2
COMMENTS
Divisible by the Catalan numbers, by the explicit formula. - F. Chapoton, Jun 24 2021
FORMULA
a(n) = binomial(2*n-2,n-1)/n * (n^2-n+1).
a(n) = binomial(2*n-2,n-1) + (n-1)*binomial(2*n-2,n).
PROG
(Sage)
[binomial(2*n-2, n-1)//n * (n**2-n+1) for n in range(1, 8)]
(PARI) a(n) = binomial(2*n-2, n-1)/n * (n^2-n+1); \\ Michel Marcus, Jun 24 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
Corrected and extended by N. J. A. Sloane, Apr 21 2000
STATUS
approved