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A131235
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Triangle read by rows: T(n,k) is number of (n-k) X k matrices, k=0..n, with nonnegative integer entries and every row and column sum <= 2.
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2
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1, 1, 1, 1, 3, 1, 1, 6, 6, 1, 1, 10, 26, 10, 1, 1, 15, 79, 79, 15, 1, 1, 21, 189, 451, 189, 21, 1, 1, 28, 386, 1837, 1837, 386, 28, 1, 1, 36, 706, 5776, 12951, 5776, 706, 36, 1, 1, 45, 1191, 15085, 66021, 66021, 15085, 1191, 45, 1, 1, 55, 1889, 34399, 258355, 551681
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,5
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REFERENCES
| R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.65(a).
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EXAMPLE
| 1; 1,1; 1,3,1; 1,6,6,1; 1,10,26,10,1; 1,15,79,79,15,1; 1,21,189,451,189,21,1; ...
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CROSSREFS
| Cf. A049088, A131236, A131237.
Sequence in context: A100862 A098568 A180959 * A202812 A157243 A146769
Adjacent sequences: A131232 A131233 A131234 * A131236 A131237 A131238
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KEYWORD
| nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 20 2007
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