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

Terms

a(0) =0a(1) =0a(2) =2a(3) =12a(4) =58a(5) =4a(6) =100a(7) =664a(8) =3514a(9) =16916a(10) =77388a(11) =343144a(12) =1490148a(13) =6376616a(14) =26992264a(15) =113317936a(16) =472661434a(17) =1961361076a(18) =8104733884a(19) =33374212936a(20) =137031378124a(21) =11497939448a(22) =94924291832a(23) =562662294608