a(n) = 2^(2n) + 2^(n-1).

Terms

a(0) =5a(1) =18a(2) =68a(3) =264a(4) =1040a(5) =4128a(6) =16448a(7) =65664a(8) =262400a(9) =1049088a(10) =4195328a(11) =16779264a(12) =67112960a(13) =268443648a(14) =1073758208a(15) =4295000064a(16) =17179934720a(17) =68719607808a(18) =274878169088