a(n) = 2^(n-2)*(2^(n+4)-(-1)^n+5).

Terms

a(0) =5a(1) =19a(2) =68a(3) =268a(4) =1040a(5) =4144a(6) =16448a(7) =65728a(8) =262400a(9) =1049344a(10) =4195328a(11) =16780288a(12) =67112960a(13) =268447744a(14) =1073758208a(15) =4295016448a(16) =17179934720a(17) =68719673344a(18) =274878169088