OFFSET
0,6
REFERENCES
F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Cambridge, 1998, p. 114 (2.4.44).
FORMULA
a(n, k) = k!*binomial(binomial(n, 2), k).
EXAMPLE
1;
1;
1, 1;
1, 3, 6, 6;
1, 6, 30, 120, 360, 720, 720;
...
KEYWORD
nonn,tabf
AUTHOR
Christian G. Bower, Jan 13 2004
EXTENSIONS
T(0,0)=1 prepended by Alois P. Heinz, Feb 14 2023
STATUS
approved