OFFSET
0,2
COMMENTS
A domicule is either a domino or it is formed by the union of two neighboring unit squares connected via their corners. In a tiling the connections of two domicules are allowed to cross each other.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..950
Index entries for linear recurrences with constant coefficients, signature (13,-21,-3).
FORMULA
G.f.: -(x^2+8*x-1)/(3*x^3+21*x^2-13*x+1).
EXAMPLE
a(1) = 5:
+---+ +---+ +---+ +---+ +---+
|o o| |o o| |o-o| |o-o| |o-o|
| X | || || | | | | | |
|o o| |o o| |o-o| |o o| |o o|
| | | | | | || || | X |
|o-o| |o-o| |o-o| |o o| |o o|
+---+ +---+ +---+ +---+ +---+.
MAPLE
gf:= -(x^2+8*x-1)/(3*x^3+21*x^2-13*x+1):
a:= n-> coeff(series(gf, x, n+1), x, n):
seq(a(n), n=0..30);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Mar 13 2014
STATUS
approved