OFFSET
1,2
COMMENTS
Column sums of the triangle in A121552.
REFERENCES
E. Barcucci, A. Del Lungo and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29- 42.
FORMULA
G.f.=Sum(P(n,t), n=1..infinity), where P[n,t]=2t^n*product(2+sum(t^i, i=1..j), j=1..n-2) [in particular, P[1,t]=t; P[2,t]=2t^2; P[3,t]=2t^3*(2+t), P[4,t]=2t^4*(2+t)(2+t+t^2)].
EXAMPLE
a(2)=2 because the only deco polyominoes of area 2 are the vertical and horizontal dominoes.
MAPLE
P:=n->2*t^n*product(2+sum(t^i, i=1..j), j=1..n-2): g:=expand(simplify(sum(P(n), n=1..36))): seq(coeff(g, t, n), n=1..32);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 16 2006
STATUS
approved