OFFSET
0,2
COMMENTS
a(n) = A181327(n,0).
Number of compositions of n into odd parts where there is 2 sorts of part 1, 4 sorts of part 3, 6 sorts of part 5, ... , 2*k sorts of part 2*k-1. - Joerg Arndt, Aug 04 2014
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
G. Castiglione, A. Frosini, E. Munarini, A. Restivo and S. Rinaldi, Combinatorial aspects of L-convex polyominoes, European J. Combin. 28 (2007), no. 6, 1724-1741.
Index entries for linear recurrences with constant coefficients, signature (2,2,0,-1).
FORMULA
G.f.: (1-z^2)^2/(1-2*z-2*z^2+z^4).
EXAMPLE
a(2)=4 because we have (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)).
MAPLE
g := (1-z^2)^2/(1-2*z-2*z^2+z^4): gser := series(g, z = 0, 32): seq(coeff(gser, z, n), n = 0 .. 30);
MATHEMATICA
CoefficientList[Series[(1 - x^2)^2/(1 - 2 x - 2 x^2 + x^4), {x, 0, 40}], x] (* Vincenzo Librandi, Aug 05 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Oct 13 2010
STATUS
approved