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

Terms

a(0) =1a(1) =0a(2) =4a(3) =2a(4) =16a(5) =14a(6) =64a(7) =74a(8) =256a(9) =350a(10) =1024a(11) =1562a(12) =4096a(13) =6734a(14) =16384a(15) =28394a(16) =65536a(17) =117950a(18) =262144a(19) =484922a(20) =1048576a(21) =1979054a(22) =4194304a(23) =8034314a(24) =16777216a(25) =32491550a(26) =67108864a(27) =131029082a(28) =268435456a(29) =527304974