Number of -1..1 arrays of n elements with first, second and third differences also in -1..1.

Terms

a(0) =3a(1) =7a(2) =13a(3) =19a(4) =27a(5) =35a(6) =47a(7) =65a(8) =91a(9) =129a(10) =185a(11) =267a(12) =387a(13) =563a(14) =821a(15) =1199a(16) =1753a(17) =2565a(18) =3755a(19) =5499a(20) =8055a(21) =11801a(22) =17291a(23) =25337a(24) =37129a(25) =54411a(26) =79739a(27) =116859a(28) =171261a(29) =250991