a(n) is the largest prime factor of 2^n + 5^n.

Terms

a(0) =2a(1) =7a(2) =29a(3) =19a(4) =641a(5) =41a(6) =541a(7) =1597a(8) =22993a(9) =397a(10) =5521a(11) =303293a(12) =380881a(13) =25117a(14) =210466621a(15) =508771a(16) =1573071713a(17) =108991369171a(18) =1343341a(20) =39558401a(21) =2525293a(22) =4807441a(23) =215038823a(24) =1173553a(25) =61001a(29) =327866809a(30) =99901