a(n) = 3*a(n-1) - 2*a(n-2) - a(n-3) + a(n-4) with n>3, a(0)=1, a(1)=2, a(2)=3, a(3)=6.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =11a(5) =20a(6) =35a(7) =60a(8) =101a(9) =168a(10) =277a(11) =454a(12) =741a(13) =1206a(14) =1959a(15) =3178a(16) =5151a(17) =8344a(18) =13511a(19) =21872a(20) =35401a(21) =57292a(22) =92713a(23) =150026a(24) =242761a(25) =392810a(26) =635595a(27) =1028430a(28) =1664051a(29) =2692508