a(n) = gcd(2^((n*(n+1)/2)) + 1, 2^n + 1).

Terms

a(0) =3a(1) =1a(2) =1a(3) =1a(4) =33a(5) =1a(6) =1a(7) =1a(8) =513a(9) =1a(10) =1a(11) =1a(12) =8193a(13) =1a(14) =1a(15) =1a(16) =131073a(17) =1a(18) =1a(19) =1a(20) =2097153a(21) =1a(22) =1a(23) =1a(24) =33554433a(25) =1a(26) =1a(27) =1a(28) =536870913a(29) =1