77232917

This number is a prime.

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The exponent in the fiftieth known Mersenne prime is a concatenation of two four-digit primes, 7723 and 2917. These primes have the same prime sum of digits, (19). Note that this is the 2nd case in which the exponent in a Mersenne prime is a concatenation of two primes with the same length. The first such case is the exponent 859433 in the 33rd Mersenne prime. [Loungrides]

The fiftieth Mersenne prime exponent is the first such exponent that starts and ends with the same prime digit. [Loungrides]