a(n) = 4*5^n - 3*4^n.

Terms

a(0) =1a(1) =8a(2) =52a(3) =308a(4) =1732a(5) =9428a(6) =50212a(7) =263348a(8) =1365892a(9) =7026068a(10) =35916772a(11) =182729588a(12) =926230852a(13) =4681485908a(14) =23608756132a(15) =118849087028a(16) =597466660612