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

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =2a(5) =4a(6) =8a(7) =15a(8) =26a(9) =48a(10) =89a(11) =163a(12) =303a(13) =564a(14) =1057a(15) =1985a(16) =3744a(17) =7084a(18) =13443a(19) =25575a(20) =48770a(21) =93206a(22) =178481a(23) =342392a(24) =657930a(25) =1266204a(26) =2440322a(27) =4709393a(28) =9099506a(29) =17602324