a(n) = 3^n + 2*n*4^(n-1).

Terms

a(0) =1a(1) =5a(2) =25a(3) =123a(4) =593a(5) =2803a(6) =13017a(7) =59531a(8) =268705a(9) =1199331a(10) =5301929a(11) =23245819a(12) =101194737a(13) =437801939a(14) =1883831161a(15) =8067412587a(16) =34402785089a(17) =146158028227a(18) =618862711113