a(0)=1, a(1)=4, a(n) = 8*a(n-1) - 14*a(n-2), n >= 2.

Terms

a(0) =1a(1) =4a(2) =18a(3) =88a(4) =452a(5) =2384a(6) =12744a(7) =68576a(8) =370192a(9) =2001472a(10) =10829088a(11) =58612096a(12) =317289536a(13) =1717746944a(14) =9299922048a(15) =50350919168a(16) =272608444672