Primes of the form 10^i + 10^j - 1.

Terms

a(0) =19a(1) =109a(2) =199a(3) =1009a(4) =1999a(5) =10009a(6) =10099a(7) =100999a(8) =199999a(9) =1000099a(10) =1000999a(11) =19999999a(12) =1000000009a(13) =1000009999a(14) =1000099999a(15) =1009999999a(16) =10000000999a(17) =10000099999a(18) =10999999999a(19) =100999999999