a(n) = 5^n - 3^n - 2*n.

Terms

a(0) =0a(1) =0a(2) =12a(3) =92a(4) =536a(5) =2872a(6) =14884a(7) =75924a(8) =384048a(9) =1933424a(10) =9706556a(11) =48650956a(12) =243609160a(13) =1219108776a(14) =6098732628a(15) =30503229188a(16) =152544843872a(17) =762810312928