id:A131892 - OEIS Search Results

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a(n) is the number of shapes of balanced trees with constant branching factor 6 and n nodes. The node is balanced if the size, measured in nodes, of each pair of its children differ by at most one node.

+0
5

1, 6, 15, 20, 15, 6, 1, 36, 540, 4320, 19440, 46656, 46656, 699840, 4374000, 14580000, 27337500, 27337500, 11390625, 91125000, 303750000, 540000000, 540000000, 288000000, 64000000, 288000000, 540000000, 540000000, 303750000, 91125000 (list; graph; listen)

	OFFSET	`1,2`
	LINKS	`Jeffrey A. Barnett Counting Balanced Tree Shapes.`
	FORMULA	`a(0) = a(1) = 1; a(6n+1+m) = (6 choose m) * a(n+1)^m * a(n)^(6-m), where n >= 0 and 0 <= m <= 6.`
	CROSSREFS	`Cf. A110316, A131889, A131890, A131891, A131893.` `Adjacent sequences: A131889 A131890 A131891 this_sequence A131893 A131894 A131895` `Sequence in context: A001484 A087110 A063266 this_sequence A045848 A044439 A128253`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jeffrey A. Barnett (jbb(AT)notatt.com), Jul 24 2007`

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Last modified October 13 09:05 EDT 2008. Contains 145008 sequences.

AT&T Labs Research