A035521 - OEIS

A035521

Fifth column of triangle A035342; related to A035330.

0, 0, 0, 0, 1, 45, 1470, 43890, 1291815, 38710035, 1199167200, 38692476900, 1304976397725, 46070080281225, 1702810398539250, 65862570279255750, 2663551451057371875, 112503209942059311375, 4957166849516125744500

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OFFSET

1,6

COMMENTS

a(n) = A035342(n,5).

a(n), n>=5, enumerates unordered n-vertex forests composed of five 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!*A035330(n-4)/(5!*2^(n-5)), n >= 5; E.g.f. ((x*c(x/2)*(1-2*x)^(-1/2))^5)/5!, where c(x) = g.f. for Catalan numbers A000108, a(0) := 0.

EXAMPLE

a(6)=45 increasing ternary 5-forest with n=6 vertices: there are three such 5-forests (four one vertex trees together with any of the three different 2-vertex trees) each with binomial(6,2)= 15 increasing labelings. W. Lang, Sep 14 2007.

CROSSREFS

Cf. A000108, A035342, A035330.

Sequence in context: A027476 A062262 A137716 * A107399 A053112 A240686

Adjacent sequences: A035518 A035519 A035520 * A035522 A035523 A035524

KEYWORD

easy,nonn

AUTHOR

Wolfdieter Lang

STATUS

approved