a(n) = [(x*y)^n] Product_{k>=1} 1/(1 - x^k + y^k).

Terms

a(0) =1a(1) =-2a(2) =4a(3) =-20a(4) =78a(5) =-282a(6) =1048a(7) =-4014a(8) =15456a(9) =-59224a(10) =227646a(11) =-879694a(12) =3407730a(13) =-13219372a(14) =51375286a(15) =-200021556a(16) =779870542a(17) =-3044448644a(18) =11898709560a(19) =-46553635346a(20) =182315752476a(21) =-714619687038