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A243206 Number of 3-matchings of the n X n grid graph. 2
0, 0, 0, 56, 1044, 6632, 26172, 78536, 196916, 434584, 871612, 1622552, 2845076, 4749576, 7609724, 11773992, 17678132, 25858616, 36967036, 51785464, 71242772, 96431912, 128628156, 169308296, 220170804, 283156952, 360472892, 454612696, 568382356, 704924744 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Number of ways 3 dominoes can be placed on an n X n chessboard.

LINKS

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

FORMULA

G.f.: 4*x^3*(-14-163*x-125*x^2-5*x^5-6*x^4+72*x^3+x^6)/(x-1)^7.

a(n) = (4*n^6-12*n^5-30*n^4+116*n^3+14*n^2-272*n+156)/3 for n>=3, a(n) = 0 for n<3.

MAPLE

a:= n-> `if`(n<3, 0, ((((((4*n-12)*n-30)*n+116)*n+14)*n-272)*n+156)/3):

seq(a(n), n=0..40);

CROSSREFS

Column k=3 of A242861.

Sequence in context: A008921 A252181 A251432 * A278675 A114059 A221802

Adjacent sequences:  A243203 A243204 A243205 * A243207 A243208 A243209

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jun 01 2014

STATUS

approved

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Last modified October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)