a(n) = 2^(n-1) - binomial(n, floor(n/2)).

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =6a(5) =12a(6) =29a(7) =58a(8) =130a(9) =260a(10) =562a(11) =1124a(12) =2380a(13) =4760a(14) =9949a(15) =19898a(16) =41226a(17) =82452a(18) =169766a(19) =339532a(20) =695860a(21) =1391720a(22) =2842226a(23) =5684452a(24) =11576916a(25) =23153832a(26) =47050564a(27) =94101128a(28) =190876696a(29) =381753392