A056728 Palindromic primes using only two distinct digits and only the exterior digit is different.

101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 13331, 15551, 16661, 19991, 72227, 75557, 76667, 78887, 79997, 1333331, 1444441, 1777771, 3222223, 3444443, 7666667, 9222229, 9888889