OFFSET
0,2
FORMULA
EXAMPLE
a(n,m) 0 1 2 3
----+--- --- --- ---
0 | 1 2 3 4
1 | 2 5 10 18
2 | 3 10 26 58
3 | 4 18 58 153
MATHEMATICA
a[n_, m_] := SeriesCoefficient[1/((1-x)^2*(1-y)^2-x*y), {x, 0, n}, {y, 0, m}];
Table[a[n-m, m], {n, 0, 10}, {m, 0, n}] // Flatten (* Jean-François Alcover, Jun 15 2017 *)
PROG
(PARI) {a(n, m) = if( n<0 || m<0, 0, polcoeff( polcoeff( -1/(x*y-sqr(1-x-y+x*y))*(1+x*O(x^n))*(1+y*O(y^k)), n), m))};
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Michael Somos, Jun 14 2017
STATUS
approved