OFFSET
0,2
COMMENTS
a(n)=Sum(A181293(n,k),k=0..n).
REFERENCES
G. Castiglione, A. Frosini, E. Munarini, A. Restivo and S. Rinaldi, Combinatorial aspects of L-convex polyominoes, European Journal of Combinatorics, 28, 2007, 1724-1741.
FORMULA
G.f. = 2z(1-z)^3/(1-4z+2z^2)^2.
a(n) = 2*A181331(n). - Emeric Deutsch, Oct 13 2010
EXAMPLE
a(2)=10 because the 2-compositions of 2, written as (top row / bottom row), are (1/1),(0/2),(2/0),(1,0/0,1),(0,1/1,0),(1,1/0,0),(0,0/1,1), having 0 + 1 + 1 + 2 + 2 + 2 + 2 = 10 zeros.
MAPLE
g := 2*z*(1-z)^3/(1-4*z+2*z^2)^2: gser := series(g, z = 0, 30): seq(coeff(gser, z, n), n = 0 .. 25);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Oct 12 2010
STATUS
approved