Expansion of 1/(1-3x-3x^3).

Terms

a(0) =1a(1) =3a(2) =9a(3) =30a(4) =99a(5) =324a(6) =1062a(7) =3483a(8) =11421a(9) =37449a(10) =122796a(11) =402651a(12) =1320300a(13) =4329288a(14) =14195817a(15) =46548351a(16) =152632917a(17) =500486202a(18) =1641103659a(19) =5381209728a(20) =17645087790a(21) =57858574347a(22) =189719352225a(23) =622093320045