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A215854 Number of simple labeled graphs on n nodes with exactly 4 connected components that are trees or cycles. 3
1, 10, 125, 1610, 23597, 394506, 7533445, 163190665, 3971678359, 107502644249, 3205669601953, 104435680520535, 3690517248021753, 140590728463023632, 5743180320999041664, 250423270549658253350, 11608409727652016747176, 570034426072900362961212 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 4..145

EXAMPLE

a(4) = 1: the graph with 4 1-node trees.

a(5) = 10: each graph has one 2-node tree and 3 1-node trees, and C(5,2) = 10.

MAPLE

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)*

      `if`(i<2, 1, i!/2 +(i+1)^(i-1)), i=0..n-k)))

    end:

a:= n-> T(n, 4):

seq(a(n), n=4..25);

CROSSREFS

Column k=4 of A215861.

The unlabeled version is A215984.

Sequence in context: A259839 A005174 A034668 * A123358 A230390 A089832

Adjacent sequences:  A215851 A215852 A215853 * A215855 A215856 A215857

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Aug 25 2012

STATUS

approved

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Last modified January 27 09:09 EST 2020. Contains 331293 sequences. (Running on oeis4.)