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

Terms

a(0) =0a(1) =2a(2) =16a(3) =98a(4) =544a(5) =2882a(6) =14896a(7) =75938a(8) =384064a(9) =1933442a(10) =9706576a(11) =48650978a(12) =243609184a(13) =1219108802a(14) =6098732656a(15) =30503229218a(16) =152544843904a(17) =762810312962