Number of third differences of arrays of length n+3 of numbers in 0..2.

Terms

a(0) =17a(1) =143a(2) =621a(3) =2059a(4) =6305a(5) =19171a(6) =58025a(7) =175099a(8) =527345a(9) =1586131a(10) =4766585a(11) =14316139a(12) =42981185a(13) =129009091a(14) =387158345a(15) =1161737179a(16) =3485735825a(17) =10458256051a(18) =31376865305a(19) =94134790219a(20) =282412759265a(21) =847255055011