id:A131890 - OEIS Search Results

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a(n) is the number of shapes of balanced trees with constant branching factor 4 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, 4, 6, 4, 1, 16, 96, 256, 256, 1536, 3456, 3456, 1296, 3456, 3456, 1536, 256, 256, 96, 16, 1, 64, 1536, 16384, 65536, 1572864, 14155776, 56623104, 84934656, 905969664, 3623878656, 6442450944, 4294967296, 17179869184, 25769803776, 17179869184 (list; graph; listen)

	OFFSET	`1,2`
	LINKS	`Jeffrey A. Barnett Counting Balanced Tree Shapes.`
	FORMULA	`a(0) = a(1) = 1; a(4n+1+m) = (4 choose m) * a(n+1)^m * a(n)^(4-m), where n >= 0 and 0 <= m <= 4.`
	CROSSREFS	`Cf. A110316, A131889, A131891, A131892, A131893.` `Sequence in context: A021687 A063422 A010670 this_sequence A062751 A135911 A164356` `Adjacent sequences: A131887 A131888 A131889 this_sequence A131891 A131892 A131893`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jeffrey A. Barnett (jbb(AT)notatt.com), Jul 24 2007`

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Last modified December 7 23:50 EST 2009. Contains 170430 sequences.

AT&T Labs Research