a(n) = n!/([(n-1)/2]!*[(n+1)/2]!) for n>0, a(0)=0, and where [ ] = floor.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =12a(5) =10a(6) =60a(7) =35a(8) =280a(9) =126a(10) =1260a(11) =462a(12) =5544a(13) =1716a(14) =24024a(15) =6435a(16) =102960a(17) =24310a(18) =437580a(19) =92378a(20) =1847560a(21) =352716a(22) =7759752a(23) =1352078a(24) =32449872a(25) =5200300a(26) =135207800a(27) =20058300a(28) =561632400a(29) =77558760