Primes composed of digit {1,9} and with digit sum 9*k+1.

Terms

a(0) =19a(1) =199a(2) =919a(3) =991a(4) =1999a(5) =9199a(6) =99991a(7) =199999a(8) =991999a(9) =999199a(10) =9999991a(11) =19999999a(12) =99991999a(13) =9199999999a(14) =11111111911a(15) =11119111111a(16) =99999199999a(17) =99999991999a(18) =111111911191a(19) =111191119111a(20) =111911191111a(21) =191119111111a(22) =991999999999a(23) =999999991999