a(n) = Product_{ceiling(n/2) <= k <= n, gcd(k,n)=1} k.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =12a(5) =5a(6) =120a(7) =35a(8) =280a(9) =63a(10) =30240a(11) =77a(12) =665280a(13) =1287a(14) =16016a(15) =19305a(16) =518918400a(17) =2431a(18) =17643225600a(19) =46189a(20) =14780480a(21) =1322685a(23) =96577a(25) =58503375a(26) =475931456000a(27) =75218625a(29) =215441