a(n) = Product_{k=1..n} k/floor(n/k).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =12a(5) =20a(6) =120a(7) =315a(8) =1680a(9) =6048a(10) =60480a(11) =138600a(12) =1663200a(13) =9266400a(14) =69189120a(15) =340540200a(16) =5448643200a(17) =22870848000a(18) =411675264000