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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =1a(6) =3a(7) =1a(8) =1a(9) =1a(10) =3a(11) =17a(12) =1a(13) =5a(14) =9a(15) =1a(16) =3a(17) =5a(18) =3a(19) =1a(20) =3a(21) =5a(22) =3a(23) =1a(24) =3a(25) =1a(26) =1a(27) =17a(28) =3a(29) =41