a(n) = 2*a(n-1) + 4*a(n-2) - 2*a(n-3) with initial terms 1, 2, 6.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =56a(5) =172a(6) =532a(7) =1640a(8) =5064a(9) =15624a(10) =48224a(11) =148816a(12) =459280a(13) =1417376a(14) =4374240a(15) =13499424a(16) =41661056a(17) =128571328a(18) =396788032a(19) =1224539264a(20) =3779088000a(21) =11662756992a(22) =35992787456a(23) =111078426880a(24) =342802489600