a(n) = (lcm_{k=0..n} (2^k + 1))/(lcm_{k=0..n-1} (2^k + 1)).

Terms

a(0) =3a(1) =5a(2) =3a(3) =17a(4) =11a(5) =13a(6) =43a(7) =257a(8) =57a(9) =205a(10) =683a(11) =241a(12) =2731a(13) =3277a(14) =331a(15) =65537a(16) =43691a(17) =4033a(18) =174763a(19) =61681a(20) =5419a(21) =838861a(22) =2796203a(23) =65281a(24) =1016801a(25) =13421773a(26) =261633a(27) =15790321a(28) =178956971a(29) =80581