A109542 - OEIS

This site is supported by donations to The OEIS Foundation.

A109542

a(n) = number of labeled 3-regular (trivalent) multi-graphs without self-loops on 2n vertices with a maximum of 2 edges between any pair of nodes. Also a(n) = number of labeled symmetric 2n X 2n matrices with {0,1,2}-entries with row sum equal to 3 for each row and trace 0.

0, 7, 640, 170555, 94949400, 95830621425, 159062872168200, 404720953797785625 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	LINKS	`Table of n, a(n) for n=1..8.`
	EXAMPLE	`a(2)=7 because for 2*n=4 nodes there are 7 possible labeled graphs whose adjacency matrices are as follows:` `0 2 1 0` `2 0 0 1` `1 0 0 2` `0 1 2 0;` `0 1 2 0` `1 0 0 2` `2 0 0 1` `0 2 1 0;` `0 2 0 1` `2 0 1 0` `0 1 0 2` `1 0 2 0;` `0 1 1 1` `1 0 1 1` `1 1 0 1` `1 1 1 0;` `0 0 2 1` `0 0 1 2` `2 1 0 0` `1 2 0 0;` `0 1 0 2` `1 0 2 0` `0 2 0 1` `2 0 1 0;` `0 0 1 2` `0 0 2 1` `1 2 0 0` `2 1 0 0.`
	CROSSREFS	`Cf. A001205, A002829, A108243.` `Sequence in context: A047942 A182346 A175601 * A052132 A052134 A101811` `Adjacent sequences: A109539 A109540 A109541 * A109543 A109544 A109545`
	KEYWORD	`nonn,more`
	AUTHOR	`Jeremy Gardiner, Aug 29 2005`
	EXTENSIONS	`a(5)-a(8) from Max Alekseyev, Aug 30 2005`
	STATUS	`approved`

Content is available under The OEIS End-User License Agreement .

Last modified May 24 07:08 EDT 2013. Contains 225617 sequences.