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A329707
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Number of placements of zero or more dominoes on a 2 X n grid where no two empty squares are horizontally adjacent.
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2
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1, 2, 4, 11, 25, 61, 146, 351, 844, 2028, 4875, 11717, 28163, 67692, 162703, 391070, 939968, 2259289, 5430383, 13052363, 31372406, 75406105, 181244648, 435636112, 1047086489, 2516756727, 6049227537, 14539805696, 34947594281, 83999358146, 201899224084, 485281049587, 1166412095721
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = 2*a(n-1) + a(n-2) - a(n-6) for n > 6.
G.f.: (1 - x)*(1 + x + x^3)/(1 - 2*x - x^2 + x^6).
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PROG
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(PARI) Vec((1 - x)*(1 + x + x^3)/(1 - 2*x - x^2 + x^6) + O(x^30))
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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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