A083998 a(1) = 3; then numbers such that the concatenation a(n)a(n-1)...a(2)a(1)a(2)...a(n-1)a(n) is a prime.

3, 1, 1, 23, 21, 3, 67, 17, 3, 39, 19, 33, 21, 39, 77, 121, 207, 9, 9, 93, 53, 1, 57, 93, 41, 339, 9, 57, 63, 1, 1091, 273, 199, 83, 213, 529, 569, 397, 21, 71, 481, 243, 111, 419, 273, 231, 63, 277, 483, 201, 531, 77, 139, 1313, 529, 1443, 587, 649, 351, 273, 189