a(n) = a(n-1) + a(n-2) + a(n-3) - a(n-4) with a(0)=0, a(1)=1, a(2)=2 and a(3)=3.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =10a(6) =17a(7) =30a(8) =51a(9) =88a(10) =152a(11) =261a(12) =450a(13) =775a(14) =1334a(15) =2298a(16) =3957a(17) =6814a(18) =11735a(19) =20208a(20) =34800a(21) =59929a(22) =103202a(23) =177723a(24) =306054a(25) =527050a(26) =907625a(27) =1563006a(28) =2691627a(29) =4635208