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

Terms

a(0) =1a(1) =1a(2) =7a(3) =23a(4) =89a(5) =329a(6) =1231a(7) =4591a(8) =17137a(9) =63953a(10) =238679a(11) =890759a(12) =3324361a(13) =12406681a(14) =46302367a(15) =172802783a(16) =644908769a(17) =2406832289a(18) =8982420391a(19) =33522849271a(20) =125108976697a(21) =466913057513