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A249846
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Number of length 2+4 0..n arrays with no five consecutive terms having the maximum of any two terms equal to the minimum of the remaining three terms.
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1
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10, 198, 1500, 6916, 23526, 65226, 156184, 335016, 659682, 1213102, 2109492, 3501420, 5587582, 8621298, 12919728, 18873808, 26958906, 37746198, 51914764, 70264404, 93729174, 123391642, 160497864, 206473080, 262938130, 331726590
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = n^6 + (9/5)*n^5 + 3*n^4 + 3*n^3 + n^2 + (1/5)*n.
G.f.: 2*x*(5 + 64*x + 162*x^2 + 112*x^3 + 17*x^4) / (1 - x)^7.
a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.
(End)
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EXAMPLE
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Some solutions for n=6
..4....5....1....0....5....0....1....6....5....3....6....5....0....5....1....5
..6....1....0....1....6....1....6....0....0....1....1....0....5....3....2....4
..5....3....4....0....3....5....3....3....2....5....6....4....2....5....0....1
..6....5....0....6....0....3....4....3....0....6....6....0....4....4....5....4
..6....0....1....4....0....0....2....0....2....5....2....4....1....3....3....2
..4....3....5....3....4....2....4....5....1....3....0....4....0....5....4....4
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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