A371660 G.f. satisfies A(x) = 1 + x * A(x)^3 * (1 + A(x) + A(x)^2).
1, 3, 36, 603, 11745, 249372, 5599044, 130735620, 3142426428, 77238209502, 1932396279066, 49047725266101, 1259884849971465, 32690034127387431, 855528520866461010, 22556952666651901761, 598607836414445357145, 15976563963437863357146
Offset: 0
Keywords
Links
- Seiichi Manyama, Table of n, a(n) for n = 0..685
Programs
-
PARI
a(n) = if(n==0, 1, sum(k=0, (n-1)\2, 3^(n-k)*binomial(n, k)*binomial(4*n-k, n-1-2*k))/n);
Formula
a(n) = (1/n) * Sum_{k=0..floor((n-1)/2)} 3^(n-k) * binomial(n,k) * binomial(4*n-k,n-1-2*k) for n > 0.