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A139263 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). 1
0, 0, 1, 3, 14, 48, 172, 580, 1941, 6373, 6373 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..10.

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.

Sequence in context: A212505 A024453 A176027 * A261043 A063025 A187917

Adjacent sequences:  A139260 A139261 A139262 * A139264 A139265 A139266

KEYWORD

nonn

AUTHOR

Lifoma Salaam, Apr 12 2008

STATUS

approved

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Last modified September 21 21:38 EDT 2018. Contains 315262 sequences. (Running on oeis4.)