OFFSET
0,5
FORMULA
G.f.: A(x, y) = Sum_{n>=0} x^n*y^n*Product(k=1..n+1} (1-k*x).
EXAMPLE
A(x,y) = (1-x) + x*y*(1-x)*(1-2*x) + x^2*y^2*(1-x)*(1-2*x)*(1-3*x) +
x^3*y^3*(1-x)*(1-2*x)*(1-3*x)*(1-4*x) + ...
Rows begin:
1;
-1,1;
0,-3,1;
0,2,-6,1;
0,0,11,-10,1;
0,0,-6,35,-15,1;
0,0,0,-50,85,-21,1;
0,0,0,24,-225,175,-28,1;
0,0,0,0,274,-735,322,-36,1;
0,0,0,0,-120,1624,-1960,546,-45,1; ...
PROG
(PARI) {T(n, k)=local(X=x+x*O(x^n), Y=y+y*O(y^k)); polcoeff(polcoeff(sum(i=0, n, X^i*Y^i*prod(j=1, i+1, 1-j*X)), n, x), k, y)}
CROSSREFS
KEYWORD
sign,tabl
AUTHOR
Paul D. Hanna, Mar 06 2005
STATUS
approved