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A243647
Number of ways four L-tiles can be placed on an n X n square.
2
0, 0, 0, 0, 1, 176, 3145, 22969, 106819, 376796, 1101151, 2805825, 6438909, 13602304, 26866541, 50186401, 89436655, 153088924, 253052339, 405702361, 633123801, 964595760, 1438347889, 2103619049, 3023051131, 4275452476, 5958967015, 8194686929, 11130748309
OFFSET
0,6
LINKS
FORMULA
G.f.: -x^4*(9*x^8 -102*x^7 +253*x^6 +179*x^5 -1340*x^4 +916*x^3 +1597*x^2 +167*x+1) / (x-1)^9.
a(n) = (n^8 -8*n^7 -14*n^6 +244*n^5 -201*n^4 -2428*n^3 +4042*n^2 +7700*n -15576) / 24 for n>=4, a(n) = 0 for n<4.
EXAMPLE
a(4) = 1:
._______.
| |_| |_|
|___|___|
| |_| |_|
|___|___| .
MAPLE
a:= n-> `if`(n<4, 0, ((((((((n-8)*n-14)*n+244)*n-201)*n
-2428)*n+4042)*n+7700)*n-15576)/24):
seq(a(n), n=0..50);
CROSSREFS
Column k=4 of A243608.
Sequence in context: A290703 A077742 A027483 * A220919 A221635 A223411
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Jun 08 2014
STATUS
approved