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A172562 Number of 3*n X n 0..1 arrays with row sums 2 and column sums 6 1
0, 1, 1680, 32496156, 2604964362000, 666569141498660400, 452489654840076972518400, 712008996110160366168717566400, 2343976695927269878444049332219968000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

REFERENCES

Gao, Shanzhen, and Matheis, Kenneth, Closed formulas and integer sequences arising from the enumeration of (0,1)-matrices with row sum two and some constant column sums. In Proceedings of the Forty-First Southeastern International Conference on Combinatorics, Graph Theory and Computing. Congr. Numer. 202 (2010), 45-53.

LINKS

R. H. Hardin, Table of n, a(n) for n=1..33

FORMULA

2^{-3n}\sum_{i=0}^{2n}\frac{(-1)^{i}(3n)!(2n)!(6n-2i)!}{% %i!(3n-i)!(2n-i)!6^{2n-i}}$ %$g(n)=4^{-2n}((2n)!)^{2}\sum_{i=0}^{2n}\frac{(-2)^{i}(4n-2i)!}{% %i!((2n-i)!)^{2}} [From Shanzhen Gao, Feb 16 2010]

CROSSREFS

Sequence in context: A234439 A060095 A156422 * A172568 A172673 A172768

Adjacent sequences:  A172559 A172560 A172561 * A172563 A172564 A172565

KEYWORD

nonn

AUTHOR

R. H. Hardin Feb 06 2010

STATUS

approved

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Last modified July 28 04:25 EDT 2014. Contains 244987 sequences.