Primes formed by concatenating k, k, and 1 for k >= 1.

Terms

a(0) =331a(1) =661a(2) =881a(3) =991a(4) =18181a(5) =20201a(6) =21211a(7) =26261a(8) =27271a(9) =32321a(10) =33331a(11) =41411a(12) =48481a(13) =51511a(14) =54541a(15) =57571a(16) =60601a(17) =65651a(18) =69691a(19) =71711a(20) =78781a(21) =86861a(22) =89891a(23) =90901a(24) =92921a(25) =98981a(26) =99991a(27) =1041041a(28) =1051051a(29) =1131131