a(n) = 2^(n-1) - ((1+(-1)^n)/4)*binomial(n, n/2).

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =5a(5) =16a(6) =22a(7) =64a(8) =93a(9) =256a(10) =386a(11) =1024a(12) =1586a(13) =4096a(14) =6476a(15) =16384a(16) =26333a(17) =65536a(18) =106762a(19) =262144a(20) =431910a(21) =1048576a(22) =1744436a(23) =4194304a(24) =7036530a(25) =16777216a(26) =28354132a(27) =67108864a(28) =114159428a(29) =268435456