OFFSET
0,2
FORMULA
a(n)=2*sum(k=1..n, (binomial(2*k-2,k-1) * sum(j=0..k, binomial(j,n-3*k+2*j) * binomial(k,j) ) )/k ), n>0, a(0)=1.
D-finite with recurrence: n*a(n) +2*(-2*n+3)*a(n-1) +4*(-n+3)*a(n-2) +2*(-2*n+9)*a(n-3)=0. - R. J. Mathar, Jan 25 2020
PROG
(Maxima)
a(n):=2*sum((binomial(2*k-2, k-1)*sum(binomial(j, n-3*k+2*j)*binomial(k, j), j, 0, k))/k, k, 1, n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Jun 03 2011
STATUS
approved