id:A139263 - OEIS Search Results

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Number of two element anti-chains in Riordan trees on n edges (also called non-redundant trees, i.e. ordered trees where no vertex has out-degree equal to 1).

+0
2

0, 0, 1, 3, 14, 48, 172, 580, 1941, 6373, 6373 (list; graph; listen)

	OFFSET	`0,4`
	FORMULA	`G.f.: A=x^2(xM+1)^3((xR)')^3(1/R) where M is the generating function for the Motzkin numbers, and R is the generating function for the Riordan numbers.`
	CROSSREFS	`Cf. A139262.` `Adjacent sequences: A139260 A139261 A139262 this_sequence A139264 A139265 A139266` `Sequence in context: A104196 A006900 A024453 this_sequence A063025 A098521 A084150`
	KEYWORD	`nonn`
	AUTHOR	`Lifoma Salaam (lifoma(AT)hotmail.com), Apr 12 2008`

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Last modified October 13 20:18 EDT 2008. Contains 145016 sequences.

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