A050711 Inserting a digit '1' between adjacent digits of n makes a prime.

13, 21, 31, 33, 37, 49, 63, 67, 69, 79, 81, 91, 99, 113, 117, 119, 123, 131, 137, 141, 159, 167, 177, 179, 183, 201, 203, 207, 209, 221, 233, 237, 239, 249, 257, 261, 263, 267, 273, 287, 291, 303, 309, 329, 339, 351, 353, 357, 387, 401, 407, 413, 417, 423