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A134645 Number of 2n X 3n (0,1,2)-matrices with every row sum 3 and column sum 2. 2
7, 16260, 747558000, 250071339672000, 369820640830881240000, 1796185853884657144990080000, 23511842995969107700302647865600000, 720289186703359375552628986978410240000000, 46455761324619133018320834819622638940550400000000, 5809177204262302555518772962193269714031251010176000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Zhonghua Tan, Shanzhen Gao, Kenneth Mathies, Joshua Fallon, Counting (0,1,2)-Matrices, Congressus Numeratium, December 2008.

LINKS

Table of n, a(n) for n=1..10.

FORMULA

Let t(m,n)=6^{-m} sum_{i=0}^{m}frac{3^{i}m!n!(2n-2i)!}{i!(m-i)!(n-i)!2^{n-i}}; then a(n) = t(2n,3n).

a(n) = (3n)!(2n)!288^(-n) * Sum_{i=0..2n} (6n-2i)!6^i/(i!(3n-i)!(2n-i)!). - Shanzhen Gao, Mar 02 2010

EXAMPLE

a(1) = 7:

111 210 (6 ways)

111 012

MAPLE

f:=proc(m, n) 6^(-m)*add( (3^i*m!*n!*(2*n-2*i)!)/ (i!*(m-i)!*(n-i)!*2^(n-i)), i=0..m); end;

CROSSREFS

Cf. A000681, A134646.

Sequence in context: A131676 A280813 A203685 * A115997 A013786 A285178

Adjacent sequences:  A134642 A134643 A134644 * A134646 A134647 A134648

KEYWORD

nonn

AUTHOR

Shanzhen Gao, Nov 05 2007

EXTENSIONS

Corrected, edited and extended with Maple program by R. H. Hardin and N. J. A. Sloane, Oct 18 2009

STATUS

approved

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Last modified June 24 07:19 EDT 2017. Contains 288697 sequences.