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A290707
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a(n) = 2^(n+1) + n^2 - 1.
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3
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1, 4, 11, 24, 47, 88, 163, 304, 575, 1104, 2147, 4216, 8335, 16552, 32963, 65760, 131327, 262432, 524611, 1048936, 2097551, 4194744, 8389091, 16777744, 33555007, 67109488, 134218403, 268436184, 536871695, 1073742664, 2147484547, 4294968256, 8589935615
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OFFSET
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0,2
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COMMENTS
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For n > 1, also the number of irredundant sets in the complete bipartite graph K_{n,n}.
For n > 1, also the number of irredundant sets in the 2 X n rook graph. - Andrew Howroyd, Aug 11 2017
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LINKS
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FORMULA
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a(n) = 2^(n+1) + n^2 - 1.
a(n) = 5*a(n-1) - 9*a(n-2) + 7*a(n-3) - 2*a(n-4).
G.f.: (x (1 - x - 2 x^3))/((-1 + x)^3 (-1 + 2 x)).
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MATHEMATICA
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Table[2^(n + 1) + n^2 - 1, {n, 0, 40}]
LinearRecurrence[{5, -9, 7, -2}, {4, 11, 24, 47}, {0, 20}]
CoefficientList[Series[(1 - x - 2 x^3)/((-1 + x)^3 (-1 + 2 x)), {x, 0, 20}], x]
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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