OFFSET
0,5
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
Wikipedia, Pentomino
FORMULA
G.f.: (4*x^20 +4*x^18 +8*x^16 -3*x^14 +4*x^13 -5*x^12 -2*x^11 +3*x^10 -2*x^9 +6*x^8 -2*x^7 +2*x^6 -2*x^5 -x^4 +2*x -1) / (-8*x^22 -28*x^20 -6*x^18 +8*x^17 +26*x^16 +4*x^15 +7*x^14 -8*x^13 -9*x^12 -14*x^11 +7*x^10 +2*x^9 +8*x^8 -2*x^7 +2*x^6 -6*x^5 +x^4 +2*x -1).
EXAMPLE
a(4) = 2:
._______. ._______.
| | ._. | | ._. | |
| |_| |_| |_| |_| |
|_. |_. | | ._| ._|
| |_| | | | | |_| |
|_____|_| |_|_____|.
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jan 01 2014
STATUS
approved