OFFSET
0,3
COMMENTS
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.
LINKS
Index entries for linear recurrences with constant coefficients, signature (7, -12, -4, 12, -4).
FORMULA
G.f. = z(1-z)^2/[(1+z)(1-4z+2z^2)^2].
EXAMPLE
a(1)=1 because in the 2-compositions of 1, namely (0/1) and (1/0) we have only one increasing column (the 2-compositions are written as (top row / bottom row).
a(2)=5 because in (0/2),(1/1),(2,0),(1,0/0,1),(0,1/1,0),(1,1/0,0), and (0,0/1,1) (the 2-compositions are written as (top row/bottom row)) we have 0+1+0+1+1+2+0=5 odd entries.
MAPLE
g := z*(1-z)^2/((1+z)*(1-4*z+2*z^2)^2): gser := series(g, z = 0, 30): seq(coeff(gser, z, k), k = 0 .. 27);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Oct 13 2010
EXTENSIONS
Edited by N. J. A. Sloane, Oct 15 2010
STATUS
approved