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Search: id:A086113
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| A086113 |
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Number of 3 X n (0,1) matrices such that each row and each column is nondecreasing or nonincreasing. |
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+0
4
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| 6, 36, 102, 216, 390, 636, 966, 1392, 1926, 2580, 3366, 4296, 5382, 6636, 8070, 9696, 11526, 13572, 15846, 18360, 21126, 24156, 27462, 31056, 34950, 39156, 43686, 48552, 53766, 59340, 65286, 71616, 78342, 85476, 93030, 101016, 109446, 118332
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Don Coppersmith, Ponder This: IBM Research Monthly Puzzles, March challenge
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FORMULA
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a(n) = 2*n*(n^2+3*n-1) = 2*n*A014209(n). More generally, number of m X n (0, 1) matrices such that each row and each column is increasing or decreasing is 2*n*(2*binomial(n+m-1, n)-m) = 2*m*(2*binomial(m+n-1, m)-n).
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CROSSREFS
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Cf. A032260, A016742, A086114, A086115.
Adjacent sequences: A086110 A086111 A086112 this_sequence A086114 A086115 A086116
Sequence in context: A044108 A080857 A108158 this_sequence A060521 A036141 A061804
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KEYWORD
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nonn
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AUTHOR
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Vladimir Baltic, Vladeta Jovovic (vladeta(AT)Eunet.yu), Jul 10 2003
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