|
|
A101276
|
|
Triangle read by rows: T(n,k) is the number of ordered trees having n edges and k branches of length 1.
|
|
0
|
|
|
1, 0, 1, 1, 0, 1, 1, 2, 0, 2, 2, 2, 6, 0, 4, 3, 8, 6, 16, 0, 9, 6, 14, 30, 16, 45, 0, 21, 11, 36, 54, 106, 45, 126, 0, 51, 22, 74, 168, 196, 360, 126, 357, 0, 127, 43, 173, 372, 706, 675, 1197, 357, 1016, 0, 323, 87, 378, 981, 1636, 2775, 2268, 3913, 1016, 2907, 0, 835, 176, 860, 2310, 4771, 6660, 10451, 7469, 12644, 2907, 8350, 0, 2188
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,8
|
|
COMMENTS
|
Row n has n+1 terms (n>=0). Row sums are the Catalan numbers (A000108). Column 0 yields A026418. T(n,n)=A001006(n-1) (n>0) (the Motzkin numbers).
|
|
LINKS
|
|
|
FORMULA
|
G.f.: G=G(t, z) satisfies z(t+z-tz)G^2-(1-z+tz+z^2-tz^2)G+1-z+tz+z^2-tz^2=0.
|
|
EXAMPLE
|
T(3,1)=2 because we have the tree with three edges hanging from the root and the tree with one edge hanging from the root at the end of which two edges are hanging.
|
|
MAPLE
|
G := 1/2/(-z^2+t*z^2-t*z)*(-1+z-t*z-z^2+t*z^2+sqrt(1-3*t^2*z^2-8*t*z^3+6*t^2*z^3+6*z^4*t-3*t^2*z^4-2*t*z-z^2-3*z^4+2*z^3-2*z+4*t*z^2)): Gser:=simplify(series(G, z=0, 13)): P[0]:=1: for n from 1 to 11 do P[n]:=coeff(Gser, z^n) od: for n from 0 to 11 do seq(coeff(t*P[n], t^k), k=1..n+1) od; # yields the sequence in triangular form
|
|
MATHEMATICA
|
m = 12; G[_] = 0;
Do[G[z_] = (1 + t z - t z^2 - z + z^2 + G[z]^2 (t z - t z^2 + z^2))/(1 + t z - t z^2 - z + z^2) + O[z]^m, {m}];
|
|
CROSSREFS
|
|
|
KEYWORD
|
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|