OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
Wikipedia, Pentomino
Index entries for linear recurrences with constant coefficients, signature (2,8,20).
FORMULA
G.f.: (4*x^3-1)/(20*x^3+8*x^2+2*x-1).
EXAMPLE
a(2) = 12:
._______. ._______. ._______. ._______.
| | | | ._| | | ._| | | ._| |
| ._| ._| |___| | | |_____| | |_____|
|_| |_| | | |___| |___| | |___|_. |
| | | | ._| | | |_. | | ._| |
|___|___| (*4) |_|_____| (*2) |_____|_| (*4) |___|___| (*2) .
MAPLE
a:= n-> ceil((<<0|1|0>, <0|0|1>, <20|8|2>>^(n-1). <<2, 12, 56>>)[1, 1]):
seq(a(n), n=0..30);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 19 2014
STATUS
approved