Numbers k such that the concatenation of k and previous_prime(k) is a prime.

Terms

a(0) =4a(1) =5a(2) =9a(3) =10a(4) =16a(5) =24a(6) =33a(7) =36a(8) =42a(9) =46a(10) =51a(11) =53a(12) =56a(13) =59a(14) =63a(15) =66a(16) =67a(17) =69a(18) =75a(19) =76a(20) =78a(21) =81a(22) =87a(23) =96a(24) =102a(25) =106a(26) =108a(27) =111a(28) =114a(29) =116