Expansion of 1/((1-x) * (1-2*x) * (1-3*x))^2.

Terms

a(0) =1a(1) =12a(2) =86a(3) =480a(4) =2307a(5) =10044a(6) =40792a(7) =157440a(8) =584693a(9) =2107596a(10) =7420218a(11) =25634880a(12) =87207559a(13) =292924668a(14) =973531964a(15) =3206704800a(16) =10482373305a(17) =34042285260a(18) =109930177630a(19) =353238247200