Prime factors of Fermat numbers.

Terms

a(0) =3a(1) =5a(2) =17a(3) =257a(4) =641a(5) =65537a(6) =114689a(7) =274177a(8) =319489a(9) =974849a(10) =2424833a(11) =6700417a(12) =13631489a(13) =26017793a(14) =45592577a(15) =63766529a(16) =167772161a(17) =825753601a(18) =1214251009a(19) =6487031809a(20) =70525124609a(21) =190274191361a(22) =646730219521