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A102003 Triangle read by rows: T(n,k) is the number of ordered trees with n edges and having k branches of odd length (n>=0, 0<=k<=n). 1
1, 0, 1, 1, 0, 1, 0, 3, 0, 2, 2, 0, 8, 0, 4, 0, 11, 0, 22, 0, 9, 5, 0, 45, 0, 61, 0, 21, 0, 41, 0, 166, 0, 171, 0, 51, 14, 0, 226, 0, 580, 0, 483, 0, 127, 0, 154, 0, 1050, 0, 1962, 0, 1373, 0, 323, 42, 0, 1070, 0, 4430, 0, 6496, 0, 3923, 0, 835, 0, 582, 0, 6005, 0, 17570, 0, 21184 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,8

COMMENTS

Row n has n+1 terms. Column 0 yields the Catalan numbers (A000108) alternating with 0's. The diagonal entries are the Motzkin numbers (A001006). T(n,n-2)=A025566(n) for n>=2.

REFERENCES

E. Deutsch, Ordered trees with prescribed root degrees, node degrees and branch lengths, Discrete Math., 282, 2004, 89-94.

J. Riordan, Enumeration of plane trees by branches and endpoints, J. Combin. Theory Ser. A 19, 1975, 214-222.

LINKS

Table of n, a(n) for n=0..73.

FORMULA

G.f.=G=G(t, z) satisfies z(t+z)G^2-(1+tz)G+1+tz=0.

EXAMPLE

T(3,3)=2 because we have (i) a tree with 3 edges hanging from the root and (ii) a tree with one edge hanging from the root, at the end of which 2 edges are hanging.

Triangle starts:

1;

0,1;

1,0,1;

0,3,0,2;

2,0,8,0,4;

MAPLE

G:=1/2/(z^2+t*z)*(t*z+1-sqrt(1-2*t*z-3*t^2*z^2-4*z^2-4*t*z^3)): Gserz:=simplify(series(G, z=0, 14)):P[0]:=1: for n from 1 to 12 do P[n]:=sort(expand(coeff(Gserz, z^n))) od: for n from 0 to 12 do seq(coeff(t*P[n], t^k), k=1..n+1) od; # yields the sequence in triangular form

CROSSREFS

Cf. A000108, A001006, A025566, A102004.

Sequence in context: A084196 A127913 A135991 * A176314 A004587 A104609

Adjacent sequences:  A102000 A102001 A102002 * A102004 A102005 A102006

KEYWORD

nonn,tabl

AUTHOR

Emeric Deutsch, Dec 23 2004

STATUS

approved

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Last modified December 9 04:50 EST 2016. Contains 278960 sequences.