Primes consisting only of digits 1 and 9 occurring with equal frequency.

Terms

a(0) =19a(1) =11919199a(2) =11919991a(3) =19111999a(4) =19199119a(5) =19911919a(6) =19991911a(7) =91919911a(8) =91999111a(9) =99111919a(10) =99119191a(11) =99919111a(12) =1111919999a(13) =1111999199a(14) =1191911999a(15) =1191919991a(16) =1191991991a(17) =1191999119a(18) =1199911919a(19) =1199911991a(20) =1199919191a(21) =1199919911a(22) =1911919199a(23) =1911991919