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Search: id:A134646
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| A134646 |
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Number of n X n (-1,0,1)-matrices with every row sum 3 and column sum 3. |
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+0
1
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OFFSET
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2,1
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REFERENCES
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Zhonghua Tan and Shanzhen Gao,Counting (0,1,2)- Matrices,submitted.
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FORMULA
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a(n) = 6^{-n} Sum_{alpha = 0 .. n} Sum_{beta = 0 .. n-alpha } \frac{(-4)^{(n-alpha -beta )}3^{beta }(n!)^{2}(beta +3alpha )!}{(alpha !)^{2}beta !(n-alpha -beta )!6^{alpha }}
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CROSSREFS
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Cf. A000681, A134645.
Sequence in context: A058244 A024235 A010789 this_sequence A004072 A113030 A030001
Adjacent sequences: A134643 A134644 A134645 this_sequence A134647 A134648 A134649
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KEYWORD
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nonn
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AUTHOR
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Shanzhen Gao (sgao2(AT)fau.edu), Nov 05 2007
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