a(n) = (2*6^n - (5^n - 3^n))/2.

Terms

a(0) =1a(1) =5a(2) =28a(3) =167a(4) =1024a(5) =6335a(6) =39208a(7) =241967a(8) =1487584a(9) =9110975a(10) =55612888a(11) =338471567a(12) =2054977744a(13) =12451139615a(14) =75314797768a(15) =454933369967