Coefficient of x^4 in (1-x-x^2)^(-n).

Terms

a(0) =5a(1) =20a(2) =51a(3) =105a(4) =190a(5) =315a(6) =490a(7) =726a(8) =1035a(9) =1430a(10) =1925a(11) =2535a(12) =3276a(13) =4165a(14) =5220a(15) =6460a(16) =7905a(17) =9576a(18) =11495a(19) =13685a(20) =16170a(21) =18975a(22) =22126a(23) =25650a(24) =29575a(25) =33930a(26) =38745a(27) =44051a(28) =49880a(29) =56265