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A035520 Fourth column of triangle A035342; related to A045894. 0
0, 0, 0, 1, 30, 705, 15960, 370125, 8998290, 231416325, 6314962500, 182894567625, 5615811951750, 182497749258825, 6264206330382000, 226636350724909125, 8624703350821808250, 344535241891693978125, 14419858385821910521500 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

a(n) = A035342(n,4).

a(n), n>=4, enumerates unordered n-vertex forests composed of four plane (ordered) increasingly labeled ternary (3-ary) trees. See A001147 (number of increasing ternary trees) and a D. Callan comment there. For a picture of some ternary trees see a W. Lang link under A001764.

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(n) = n!*A045894(n-4)/(4!*2^(n-4)), n >= 4; E.g.f. ((x*c(x/2)/(1-2*x)^(1/2))^4)/4!, where c(x) = g.f. for Catalan numbers A000108, a(0) := 0.

EXAMPLE

a(5)=30 increasing ternary 4-forest with n=5 vertices: there are three such 4-forests (three one vertex trees together with any of the three different 2-vertex trees) each with 10 increasing labelings. Wolfdieter Lang, Sep 14 2007.

CROSSREFS

Cf. A035342, A045894.

Sequence in context: A152499 A027475 A180801 * A122186 A166840 A166828

Adjacent sequences:  A035517 A035518 A035519 * A035521 A035522 A035523

KEYWORD

easy,nonn

AUTHOR

Wolfdieter Lang

STATUS

approved

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Last modified February 17 14:12 EST 2018. Contains 299296 sequences. (Running on oeis4.)