Expansion of Product_{k=0..3} (1 + k*x)/(1 - k*x).

Terms

a(0) =1a(1) =12a(2) =72a(3) =312a(4) =1152a(5) =3912a(6) =12672a(7) =39912a(8) =123552a(9) =378312a(10) =1150272a(11) =3481512a(12) =10505952a(13) =31640712a(14) =95167872a(15) =285995112a(16) =858968352a(17) =2578871112a(18) =7740545472a(19) =23229500712a(20) =69704230752a(21) =209144149512a(22) =627495363072