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

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =10a(5) =22a(6) =44a(7) =93a(8) =186a(9) =386a(10) =772a(11) =1586a(12) =3172a(13) =6476a(14) =12952a(15) =26333a(16) =52666a(17) =106762a(18) =213524a(19) =431910a(20) =863820a(21) =1744436a(22) =3488872a(23) =7036530a(24) =14073060a(25) =28354132a(26) =56708264a(27) =114159428a(28) =228318856a(29) =459312152