a(0) = 1, a(1) = 0, a(2) = a(3) = 1; thereafter, a(n) = a(n-1) + a(n-2) + a(n-4).

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =3a(5) =4a(6) =8a(7) =13a(8) =24a(9) =41a(10) =73a(11) =127a(12) =224a(13) =392a(14) =689a(15) =1208a(16) =2121a(17) =3721a(18) =6531a(19) =11460a(20) =20112a(21) =35293a(22) =61936a(23) =108689a(24) =190737a(25) =334719a(26) =587392a(27) =1030800a(28) =1808929a(29) =3174448