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A215773
Number of undirected labeled graphs on n+3 nodes with exactly n cycle graphs as connected components.
2
0, 3, 25, 120, 420, 1190, 2898, 6300, 12540, 23265, 40755, 68068, 109200, 169260, 254660, 373320, 534888, 750975, 1035405, 1404480, 1877260, 2475858, 3225750, 4156100, 5300100, 6695325, 8384103, 10413900, 12837720, 15714520, 19109640, 23095248, 27750800
OFFSET
0,2
LINKS
FORMULA
G.f.: (8*x^2+4*x+3)*x/(1-x)^7.
a(n) = n*(n+1)*(n+2)*(n+3)*(n^2+n+4)/48.
EXAMPLE
a(1) = 3: .1-2. .1.2. .1-2.
. .|.|. .|X|. ..X..
. .3-4. .3.4. .3-4.
MAPLE
a:= n-> (24+(50+(41+(21+(7+n)*n)*n)*n)*n)*n/48:
seq (a(n), n=0..40);
CROSSREFS
A diagonal of A215771.
Sequence in context: A059457 A165206 A095664 * A377555 A099868 A243228
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Aug 23 2012
STATUS
approved