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This number is a prime.

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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]