Constant term in the expansion of (1 + x^3 + y^3 + 1/(x*y))^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =21a(6) =121a(7) =421a(8) =1121a(9) =2521a(10) =6301a(11) =23101a(12) =99001a(13) =386101a(14) =1301301a(15) =3943941a(16) =11779041a(17) =38241841a(18) =136988041a(19) =504616441a(20) =1793870941a(21) =6061831441a(22) =19923689941a(23) =66139128441a(24) =227052188441a(25) =800641330721