Expansion of (1+x) / (1-2*x-6*x^2).

Terms

a(0) =1a(1) =3a(2) =12a(3) =42a(4) =156a(5) =564a(6) =2064a(7) =7512a(8) =27408a(9) =99888a(10) =364224a(11) =1327776a(12) =4840896a(13) =17648448a(14) =64342272a(15) =234575232a(16) =855204096a(17) =3117859584a(18) =11366943744a(19) =41441044992a(20) =151083752448a(21) =550813774848