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

Terms

a(0) =9a(1) =49a(2) =199a(3) =665a(4) =2059a(5) =6305a(6) =19171a(7) =58025a(8) =175099a(9) =527345a(10) =1586131a(11) =4766585a(12) =14316139a(13) =42981185a(14) =129009091a(15) =387158345a(16) =1161737179a(17) =3485735825a(18) =10458256051a(19) =31376865305a(20) =94134790219a(21) =282412759265a(22) =847255055011