a(n) = lcm(1,2,...,2*n) / (n*binomial(2*n, n)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =2a(5) =5a(6) =15a(7) =7a(8) =28a(9) =126a(10) =30a(11) =165a(12) =198a(13) =143a(14) =1001a(15) =15015a(16) =3640a(17) =884a(18) =7956a(19) =1938a(20) =19380a(21) =203490a(22) =49742a(23) =572033a(24) =980628a(25) =240350a(26) =3124550a(27) =766935a(28) =188370a(29) =2731365