Primes remaining prime if all but two digits are deleted.

Terms

a(0) =11a(1) =13a(2) =17a(3) =19a(4) =23a(5) =29a(6) =31a(7) =37a(8) =41a(9) =43a(10) =47a(11) =53a(12) =59a(13) =61a(14) =67a(15) =71a(16) =73a(17) =79a(18) =83a(19) =89a(20) =97a(21) =113a(22) =131a(23) =137a(24) =173a(25) =179a(26) =197a(27) =311a(28) =317a(29) =431