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A360874
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Number of (non-null) connected induced subgraphs in the 2 X n rook graph.
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3
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3, 13, 51, 205, 843, 3493, 14451, 59485, 243483, 991573, 4021251, 16253965, 65530923, 263685253, 1059458451, 4252051645, 17050991163, 68332580533, 273716694051, 1096026940525, 4387590352203, 17560813373413, 70274617776051, 281192580728605, 1125052685342043
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 10*a(n-1) - 35*a(n-2) + 50*a(n-3) - 24*a(n-4) for n > 4.
G.f.: x*(3 - 17*x + 26*x^2)/((1 - x)*(1 - 2*x)*(1 - 3*x)*(1 - 4*x)).
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PROG
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(PARI) Vec((3 - 17*x + 26*x^2)/((1 - x)*(1 - 2*x)*(1 - 3*x)*(1 - 4*x)) + O(x^25))
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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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