OFFSET
0,3
LINKS
P. Flajolet and R. Sedgewick, Analytic Combinatorics, 2009; page 340.
FORMULA
O.g.f.: (1 - 7*x^2)/(1 - 7*x^2 - 3*y*x^2 + 9*y*x^4).
EXAMPLE
Triangle T(n,k) begins:
1;
0, 3;
0, 12, 9;
0, 84, 72, 27;
0, 588, 648, 324, 81;
...
MATHEMATICA
Table[nn = n; CoefficientList[Series[(1 - 7 z^2)/(1 - (7 + 3 u) z^2 + 9 u z^4), {z, 0, nn}], {z, u}][[-1]], {n, 0, 15, 2}] // Grid
CROSSREFS
KEYWORD
AUTHOR
Geoffrey Critzer, Jul 29 2020
STATUS
approved