OFFSET
0,2
FORMULA
a(n) = Sum[ Binomial[2k, k] Trinomial[n, k], {k, 0, 2n} ] where Trinomial[n, k] = trinomial coefficients (A027907)
a(n)=sum{k=0..n, sum{j=0..n, C(n, j)C(j, k)C(2(j+k), j+k)}}; - Paul Barry, Feb 15 2005
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Emanuele Munarini, May 21 2003
STATUS
approved