a(n) = Product_{k=1..n-1} gcd(k,n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =12a(6) =1a(7) =16a(8) =9a(9) =80a(10) =1a(11) =3456a(12) =1a(13) =448a(14) =2025a(15) =2048a(16) =1a(17) =186624a(18) =1a(19) =1024000a(20) =35721a(21) =11264a(22) =1a(23) =573308928a(24) =625a(25) =53248a(26) =59049a(27) =179830784a(28) =1a(30) =1