OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..80
FORMULA
a(n) = Sum_{k=0..n} [x^n*y^k] 1/2 * Product_{i,j>=0} (1+x^i*y^j).
EXAMPLE
a(2) = 9: [(2,0)], [(2,1)], [(2,0),(0,1)], [(1,1),(1,0)], [(2,2)], [(2,1),(0,1)], [(2,0),(0,2)], [(1,2),(1,0)], [(1,1),(1,0),(0,1)].
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 22 2012
STATUS
approved