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 A121445 Triangle read by rows: T(n,k) is the number of ternary trees with n edges and such that the first leaf in the preorder traversal is at level k (1<=k<=n). A ternary tree is a rooted tree in which each vertex has at most three children and each child of a vertex is designated as its left or middle or right child. 3
 3, 3, 9, 10, 18, 27, 42, 69, 81, 81, 198, 312, 351, 324, 243, 1001, 1540, 1701, 1566, 1215, 729, 5304, 8034, 8784, 8100, 6480, 4374, 2187, 29070, 43554, 47313, 43713, 35640, 25515, 15309, 6561, 163438, 242896, 262684, 243108, 200745, 148716, 96957 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Sum of terms in row n is A001764(n+1). T(n,1)=A121446(n) Sum(k*T(n,k),k=1..n)=A121447(n). LINKS Table of n, a(n) for n=1..43. FORMULA G.f.=G=G(t,z)=1/[1-t(h-1-z)/(h-1)]-1, where h=1+zh^3=2sin(arcsin(sqrt(27z/4))/3)/sqrt(3z). EXAMPLE T(1,1)=3 because we have the trees /, | and \. T(2,1)=3 because we have the trees /|, /\ and |\. Triangle starts: 3; 3,9; 10,18,27; 42,69,81; 198,312,351,324,243; MAPLE h:=2/sqrt(3*z)*sin(arcsin(sqrt(27*z/4))/3): G:=rationalize(1/(1-t*(h-1-z)/(h-1)))-1: Gser:=simplify(series(G, z=0, 18)): for n from 1 to 10 do P[n]:=sort(expand(coeff(Gser, z^n))) od: for n from 1 to 10 do seq(coeff(P[n], t, j), j=1..n) od; # yields sequence in triangular form CROSSREFS Cf. A001764, A121446, A121447. Sequence in context: A232281 A223743 A117783 * A327798 A121074 A121072 Adjacent sequences: A121442 A121443 A121444 * A121446 A121447 A121448 KEYWORD nonn,tabf AUTHOR Emeric Deutsch, Jul 30 2006 EXTENSIONS Keyword tabl changed to tabf by Michel Marcus, Apr 09 2013 STATUS approved

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Last modified July 13 20:42 EDT 2024. Contains 374288 sequences. (Running on oeis4.)