Largest prime factor of 4^n + 1.

Terms

a(0) =2a(1) =5a(2) =17a(3) =13a(4) =257a(5) =41a(6) =241a(7) =113a(8) =65537a(9) =109a(10) =61681a(11) =2113a(12) =673a(13) =1613a(14) =15790321a(15) =1321a(16) =6700417a(17) =26317a(18) =38737a(19) =525313a(20) =4278255361a(21) =14449a(22) =2931542417a(23) =30269a(24) =22253377a(25) =268501a(26) =308761441a(27) =279073a(28) =54410972897a(29) =536903681