OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
Wikipedia, Pentomino
FORMULA
G.f.: -(x^10 +x^8 -x^6 -6*x^5 -x^4 -5*x^3 +1) / (x^15 +x^13 -2*x^11 -11*x^10 -2*x^9 -10*x^8 +x^7 +9*x^6 +12*x^5 +8*x^4 +11*x^3 +x -1).
EXAMPLE
a(3) = 7:
._____. ._____. ._____. ._____. ._____. ._____. ._____.
|_|_|_| | |_| | | ._. | | ._| |_. | | |_| |_| |
|_|_|_| |_____| |_|_|_| |___|_| |_|___| |_____| |_____| .
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Nov 29 2016
STATUS
approved