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A215851 Number of simple labeled graphs on n nodes with exactly 1 connected component that is a tree or a cycle. 3
1, 1, 4, 19, 137, 1356, 17167, 264664, 4803129, 100181440, 2359762091, 61937322624, 1792399894837, 56697025885696, 1946238657504975, 72058247875111936, 2862433512904759793, 121439708940308299776, 5480390058971655049939, 262144060822550204416000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..150

FORMULA

a(1) = a(2) = 1, a(n) = A000272(n) + A001710(n-1) = n^(n-2) + (n-1)!/2 for n>2.

EXAMPLE

a(3) = 4:

.1-2.  .1-2.  .1-2.  .1 2.

.|/ .  .|  .  . / .  .|/ .

.3...  .3...  .3...  .3...

MAPLE

a:= n-> `if`(n<3, 1, (n-1)!/2+n^(n-2)):

seq(a(n), n=1..25);

CROSSREFS

Column k=1 of A215861.

The unlabeled version is A215981.

Cf. A000272, A001710.

Sequence in context: A157303 A007788 A259354 * A197920 A208811 A305725

Adjacent sequences:  A215848 A215849 A215850 * A215852 A215853 A215854

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Aug 25 2012

STATUS

approved

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Last modified February 27 21:47 EST 2020. Contains 332310 sequences. (Running on oeis4.)