OFFSET
2,2
COMMENTS
a(n) = Sum_{k>=1} A181368(n,k).
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.
G. Castiglione and A. Restivo, Reconstruction of L-convex polyominoes, Electronic Notes in Discrete Mathematics, Vol. 12, Elsevier Science, 2003.
LINKS
Index entries for linear recurrences with constant coefficients, signature (8,-20,16,-4).
FORMULA
G.f. = z^2*(1-z)^6/(1-4z+2z^2)^2.
EXAMPLE
a(3)=2 because the L-convex polyominoes of semiperimeter 3 are the horizontal and the vertical dominoes, each containing one maximal rectangle.
MAPLE
g := z^2*(1-z)^6/(1-4*z+2*z^2)^2: gser := series(g, z = 0, 32): seq(coeff(gser, z, n), n = 2 .. 28);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Oct 17 2010
STATUS
approved