a(1) = 1; thereafter a(n) is the product of all 0 < m < n for which n == a(m) (mod m).

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =24a(5) =1a(6) =12a(7) =3a(8) =40a(9) =1a(10) =480a(11) =7a(12) =432a(13) =15a(14) =28a(15) =13a(16) =24a(17) =11a(18) =40320a(19) =3a(20) =1520a(21) =9a(22) =120a(23) =85a(24) =48a(25) =21a(26) =16a(27) =345a(28) =1452971520a(29) =1