OFFSET
0,1
COMMENTS
A tatami tiling consists of dimers (1 X 2) and monomers (1 X 1) where no four meet at a point.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
A. Erickson, F. Ruskey, M. Schurch and J. Woodcock, Monomer-Dimer Tatami Tilings of Rectangular Regions, Electronic Journal of Combinatorics, 18(1) (2011) P109, 24 pages.
FORMULA
G.f.: 2 * Product_{k>0} (1 + x^k)^2.
a(n) = 2 * A022567(n).
EXAMPLE
a(0) = 2 because exactly 2 tilings are possible for 0 horizontal dimers and any m >= 2. For example, with m = 3:
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MAPLE
gf:= n-> 2 * mul((1 + x^k)^2, k=1..n):
a:= n-> coeff(series(gf(n), x, n+1), x, n):
seq(a(n), n=0..60); # Alois P. Heinz, Jul 15 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Frank Ruskey and Yuji Yamauchi (eugene.uti(AT)gmail.com), Jul 15 2011
STATUS
approved