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

Terms

a(0) =1a(1) =4a(2) =14a(3) =45a(4) =139a(5) =422a(6) =1272a(7) =3823a(8) =11477a(9) =34440a(10) =103330a(11) =310001a(12) =930015a(13) =2790058a(14) =8370188a(15) =25110579a(16) =75331753a(17) =225995276a(18) =677985846a(19) =2033957557a(20) =6101872691a(21) =18305618094a(22) =54916854304a(23) =164750562935a(24) =494251688829