A084670 Numbers n such that concatenation of prime[n] and n is prime.

3, 9, 19, 21, 37, 63, 77, 81, 87, 107, 121, 133, 177, 201, 211, 213, 217, 281, 293, 303, 321, 327, 329, 333, 351, 391, 393, 439, 481, 503, 507, 519, 543, 547, 551, 561, 579, 581, 599, 621, 639, 657, 663, 667