a(n) = B(2*n, 2)/B(2*n) (see formula section).

Terms

a(0) =1a(1) =10a(2) =46a(3) =190a(4) =766a(5) =3070a(6) =12286a(7) =49150a(8) =196606a(9) =786430a(10) =3145726a(11) =12582910a(12) =50331646a(13) =201326590a(14) =805306366a(15) =3221225470a(16) =12884901886a(17) =51539607550a(18) =206158430206a(19) =824633720830