12345678911223344556677

This number is a prime.

                                                   123 4567891122 3344556677

The smallest prime formed from the concatenation in order of first n positive repdigit numbers, (n=16). Note that the sum of these repdigit numbers, i.e., 1+2+3+4+5+6+7+8+9+11+22+33+44+55+66+77=353, is the smallest prime-digit palindromic prime. [Loungrides]