a(n) = (10^n + 6^n)/2.

Terms

a(0) =1a(1) =8a(2) =68a(3) =608a(4) =5648a(5) =53888a(6) =523328a(7) =5139968a(8) =50839808a(9) =505038848a(10) =5030233088a(11) =50181398528a(12) =501088391168