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A215764
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Number of undirected labeled graphs on n nodes with exactly 4 cycle graphs as connected components.
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2
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1, 10, 65, 420, 3157, 27342, 264925, 2831455, 33077539, 419262987, 5730379473, 84009491475, 1315019717433, 21890336017248, 386143234692768, 7195289865439824, 141228388872794736, 2912462945497687680, 62959048637195335680, 1423638554827333204800
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OFFSET
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4,2
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LINKS
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EXAMPLE
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a(4) = 1: o1.2o
. .....
. o3.4o
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MAPLE
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T:= proc(n, k) option remember; `if`(k<0 or k>n, 0, `if`(n=0, 1,
add(binomial(n-1, i)*T(n-1-i, k-1)*ceil(i!/2), i=0..n-k)))
end:
a:= n-> T(n, 4):
seq (a(n), n=4..25);
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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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