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A221526
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Number of 0..n arrays of length 6 with each element differing from at least one neighbor by 2 or more.
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1
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0, 10, 274, 2172, 9982, 33380, 90684, 212812, 447962, 867012, 1569640, 2691164, 4410102, 6956452, 10620692, 15763500, 22826194, 32341892, 44947392, 61395772, 82569710, 109495524, 143357932, 185515532, 237517002, 301118020, 378298904
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 1*n^6 - 20*n^4 + 83*n^3 - 182*n^2 + 236*n - 148 for n>3.
G.f.: 2*x^2*(5 + 102*x + 232*x^2 + 91*x^3 - 61*x^4 + 3*x^5 - 15*x^6 + 4*x^7 - x^8) / (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>10.
(End)
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EXAMPLE
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Some solutions for n=6:
..0....6....6....3....0....5....0....1....5....5....3....4....0....0....1....6
..5....1....1....0....4....1....6....3....2....3....0....1....5....6....5....0
..6....2....1....0....6....3....0....5....2....0....6....5....6....0....2....6
..1....6....6....2....5....5....5....1....4....5....3....2....0....2....0....0
..5....2....2....3....3....5....1....3....0....3....1....0....6....3....0....5
..3....0....4....6....5....0....4....6....2....5....4....5....4....1....5....2
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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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