Let 2^k = smallest power of 2 >= binomial(n,[n/2]); a(n) = 2^k - binomial(n,[n/2]).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =6a(6) =12a(7) =29a(8) =58a(9) =2a(10) =4a(11) =50a(12) =100a(13) =332a(14) =664a(15) =1757a(16) =3514a(17) =8458a(18) =16916a(19) =38694a(20) =77388a(21) =171572a(22) =343144a(23) =745074a(24) =1490148a(25) =3188308a(26) =6376616a(27) =13496132a(28) =26992264a(29) =56658968