Primes dividing repunits R(10^n) for some n.

Terms

a(0) =11a(1) =17a(2) =41a(3) =73a(4) =101a(5) =137a(6) =251a(7) =257a(8) =271a(9) =353a(10) =401a(11) =449a(12) =641a(13) =751a(14) =1201a(15) =1409a(16) =1601a(17) =3541a(18) =4001a(19) =4801a(20) =5051a(21) =9091a(22) =10753a(23) =15361a(24) =16001a(25) =19841a(26) =21001a(27) =21401a(28) =24001a(29) =25601