

A134646


Number of n X n (0,1,2)matrices with every row sum 3 and column sum 3.


3



0, 2, 31, 1344, 111920, 16214000, 3758757240, 1310799454720, 655551508577280, 452647176631372800, 418399785559398720000, 504669505260741099417600, 777461035821119354357452800, 1501959201213688265322501427200
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OFFSET

1,2


REFERENCES

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


LINKS

R. H. Hardin, Table of n, a(n) for n=1..99


FORMULA

a(n) = 6^{n} Sum_{alpha = 0 .. n} Sum_{beta = 0 .. nalpha } \frac{(4)^{(nalpha beta )}3^{beta }(n!)^{2}(beta +3alpha )!}{(alpha !)^{2}beta !(nalpha beta )!6^{alpha }}


EXAMPLE

a(2) = 2:
21 12
12 21


CROSSREFS

Cf. A000681, A134645.
Sequence in context: A246970 A246969 A358567 * A197320 A239332 A350940
Adjacent sequences: A134643 A134644 A134645 * A134647 A134648 A134649


KEYWORD

nonn,easy


AUTHOR

Shanzhen Gao, Nov 05 2007


EXTENSIONS

Definition corrected and a(7) and a(8) found (by direct enumeration) by R. H. Hardin, Oct 18 2009
a(9)  a(99) from R. H. Hardin Feb 06 2010


STATUS

approved



