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A100136
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a(n) = Sum_{k=0..floor(n/6)} C(n-3k,3k) * 3^k.
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4
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1, 1, 1, 1, 1, 1, 4, 13, 31, 61, 106, 169, 262, 424, 748, 1417, 2749, 5251, 9709, 17395, 30553, 53434, 94285, 168859, 306283, 558742, 1017895, 1844044, 3320044, 5952472, 10660177, 19119385, 34383781, 61985497, 111884665, 201938701, 364128136
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OFFSET
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0,7
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LINKS
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FORMULA
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G.f.: (1-x)^2/((1-x)^3 - 3x^6).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) + 3*a(n-6).
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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