A243464 Number of ways 2 domicules can be placed on an n X n square.

0, 0, 3, 110, 657, 2172, 5375, 11178, 20685, 35192, 56187, 85350, 124553, 175860, 241527, 324002, 425925, 550128, 699635, 877662, 1087617, 1333100, 1617903, 1946010, 2321597, 2749032, 3232875, 3777878, 4388985, 5071332, 5830247, 6671250, 7600053, 8622560

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Formula

G.f.: x^2*(43*x^3-137*x^2-95*x-3)/(x-1)^5.

a(n) = -43+63*n-4*n^2-24*n^3+8*n^4 for n>0, a(0) = 0.

Example

a(2) = 3:
+---+  +---+  +---+
|o-o|  |o o|  |o o|
|   |  || ||  | X |
|o-o|  |o o|  |o o|
+---+  +---+  +---+.

Maple

a:= n-> `if`(n=0, 0, (((8*n-24)*n-4)*n+63)*n-43):
seq(a(n), n=0..50);

Crossrefs

Column k=2 of A243424.

Sequence in context: A092252 A338472 A201001 * A114738 A111091 A301612

Adjacent sequences: A243461 A243462 A243463 * A243465 A243466 A243467

Keyword

nonn,easy

Author

Alois P. Heinz, Jun 05 2014

Status

approved