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A222939
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Number of n X 1 0..4 arrays with no element equal to another at a city block distance of exactly two, and new values 0..4 introduced in row major order.
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1
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1, 2, 3, 7, 20, 66, 238, 902, 3510, 13846, 54998, 219222, 875350, 3498326, 13987158, 55936342, 223720790, 894834006, 3579237718, 14316754262, 57266623830, 229065708886, 916261262678, 3665041904982, 14660161328470, 58640632730966
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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) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3) for n>5.
G.f.: x*(1 + x)*(1 - 6*x + 9*x^2 - 3*x^3) / ((1 - x)*(1 - 2*x)*(1 - 4*x)).
a(n) = (256 + 9*2^(3+n) + 5*4^n) / 384 for n>2.
(End)
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EXAMPLE
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All solutions for n=3:
..0....0....0
..0....1....1
..1....2....1
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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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