a(0) = 2, a(n) = 3*a(n-1) - 3.

Terms

a(0) =2a(1) =3a(2) =6a(3) =15a(4) =42a(5) =123a(6) =366a(7) =1095a(8) =3282a(9) =9843a(10) =29526a(11) =88575a(12) =265722a(13) =797163a(14) =2391486a(15) =7174455a(16) =21523362a(17) =64570083a(18) =193710246a(19) =581130735a(20) =1743392202a(21) =5230176603a(22) =15690529806a(23) =47071589415a(24) =141214768242a(25) =423644304723