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A212836
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Number of 0..n arrays of length 3 with 0 never adjacent to n.
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1
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2, 17, 50, 107, 194, 317, 482, 695, 962, 1289, 1682, 2147, 2690, 3317, 4034, 4847, 5762, 6785, 7922, 9179, 10562, 12077, 13730, 15527, 17474, 19577, 21842, 24275, 26882, 29669, 32642, 35807, 39170, 42737, 46514, 50507, 54722, 59165, 63842, 68759, 73922
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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^3 + 3*n^2 - n - 1.
G.f.: x*(2 + 9*x - 6*x^2 + x^3) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4.
(End)
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EXAMPLE
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Some solutions for n=5:
..4....1....2....5....0....3....4....2....4....0....2....5....4....3....1....1
..4....2....4....1....3....5....2....1....3....0....4....4....4....2....3....2
..2....1....3....5....3....1....4....4....5....3....2....3....1....2....0....0
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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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