131

This number is a prime.

131 is the smallest pallindromic prime that remains so by inserting the following same digit d six times between its adjacent digits, one at a time, for d = 0, 1, 3, 4, 6, 9 (6 times): 10301 = prime 11311 = prime 13331 = prime 14341 = prime 16361 = prime 19391 = prime. [Rivera]