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

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =8a(5) =21a(6) =49a(7) =120a(8) =288a(9) =697a(10) =1681a(11) =4060a(12) =9800a(13) =23661a(14) =57121a(15) =137904a(16) =332928a(17) =803761a(18) =1940449a(19) =4684660a(20) =11309768a(21) =27304197a(22) =65918161a(23) =159140520a(24) =384199200a(25) =927538921a(26) =2239277041a(27) =5406093004a(28) =13051463048a(29) =31509019101