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

Terms

a(0) =1a(1) =6a(2) =4a(3) =24a(4) =16a(5) =96a(6) =64a(7) =384a(8) =256a(9) =1536a(10) =1024a(11) =6144a(12) =4096a(13) =24576a(14) =16384a(15) =98304a(16) =65536a(17) =393216a(18) =262144a(19) =1572864a(20) =1048576a(21) =6291456a(22) =4194304a(23) =25165824a(24) =16777216a(25) =100663296a(26) =67108864a(27) =402653184a(28) =268435456a(29) =1610612736