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

Terms

a(0) =2a(1) =3a(2) =5a(3) =13a(4) =17a(5) =181a(6) =65a(7) =1873a(8) =1601a(9) =22033a(10) =1025a(11) =110120401a(12) =4097a(13) =3032641a(14) =46240001a(15) =6563711233a(16) =65537a(18) =262145a(20) =270400000001a(21) =61977830401a(22) =4194305a(24) =87578116097