OFFSET
0,3
LINKS
FORMULA
a(n) = sum(k=1..n, sum(i=k..n,(sum(j=0..k, binomial(j,-3*k+2*j+i)* 3^(-3*k+2*j+i)*2^(k-j)*binomial(k,j)))*binomial(n+k-i-1,k-1))), n>0, a(0)=1. - Vladimir Kruchinin, May 05 2011
MATHEMATICA
CoefficientList[Series[(1-x)/(1-2*x-3*x^2-2*x^3), {x, 0, 30}], x] (* or *) LinearRecurrence[{2, 3, 2}, {1, 1, 5}, 30] (* Harvey P. Dale, Oct 11 2017 *)
PROG
(Maxima)
a(n):=sum(sum((sum(binomial(j, -3*k+2*j+i)*3^(-3*k+2*j+i)*2^(k-j)*binomial(k, j), j, 0, k))*binomial(n+k-i-1, k-1), i, k, n), k, 1, n); /* Vladimir Kruchinin, May 05 2011 */
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 17 2002
STATUS
approved