a(n)=2*3^n - 18*4^n + 24*5^n.

Terms

a(0) =8a(1) =54a(2) =330a(3) =1902a(4) =10554a(5) =57054a(6) =302730a(7) =1584462a(8) =8208474a(9) =42195774a(10) =215618730a(11) =1096731822a(12) =5558447994a(13) =28092104094a(14) =141662102730a(15) =713123219982