Coefficient of x^n in the expansion of 1 / (1-x-x^3)^n.

Terms

a(0) =1a(1) =1a(2) =3a(3) =13a(4) =55a(5) =231a(6) =987a(7) =4278a(8) =18711a(9) =82390a(10) =364793a(11) =1622556a(12) =7244419a(13) =32449158a(14) =145747290a(15) =656199048a(16) =2960596359a(17) =13382107227a(18) =60587421882a(19) =274712295550