OFFSET
1,2
LINKS
E. Deutsch and M. Noy, Statistics on non-crossing trees, Discrete Math., 254 (2002), 75-87.
FORMULA
T(n, k) = (k+1)binomial(3n-k-2, 2n-1) (0<=k<=n-1).
EXAMPLE
T(2,1)=2 because in the non-crossing trees /_, _\ and /\ we have 2 nonroot nodes of outdegree 1.
Triangle begins:
1;
4,2;
21,12,3;
120,72,24,4;
MAPLE
for n from 1 to 10 do seq((k+1)*binomial(3*n-k-2, 2*n-1), k=0..n-1) od; # yields sequence in triangular form
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Emeric Deutsch, Dec 30 2004
STATUS
approved