A368934 Expansion of (1/x) * Series_Reversion( x * (1-x)^2 * (1-x-x^2) ).
1, 3, 16, 104, 751, 5789, 46656, 388377, 3313304, 28816513, 254548840, 2277498340, 20596833817, 187974816142, 1729033498416, 16012809644088, 149186508912927, 1397300099214753, 13149137686976324, 124262625068365924, 1178796712807563025
Offset: 0
Keywords
Programs
-
PARI
a(n) = sum(k=0, n\2, binomial(n+k, k)*binomial(4*n-k+2, n-2*k))/(n+1);
-
PARI
my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x)^2*(1-x-x^2))/x)
Formula
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} binomial(n+k,k) * binomial(4*n-k+2,n-2*k).