Number of 0..n arrays of length 4 with 0 never adjacent to n.

Terms

a(0) =2a(1) =41a(2) =178a(3) =497a(4) =1106a(5) =2137a(6) =3746a(7) =6113a(8) =9442a(9) =13961a(10) =19922a(11) =27601a(12) =37298a(13) =49337a(14) =64066a(15) =81857a(16) =103106a(17) =128233a(18) =157682a(19) =191921a(20) =231442a(21) =276761a(22) =328418a(23) =386977a(24) =453026a(25) =527177a(26) =610066a(27) =702353a(28) =804722a(29) =917881