131

This number is a prime.

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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]

131 is the smallest prime fully auto-insertable (into all of its internal positions), one at a time. Accordingly, the following two integers are primes: 1'131'31, 13'131'1 [Rivera]