This number is a prime.

+ This prime is the concatenation of the Sophie Germain prime p=23 and the corresponding safe prime 2p+1. It is the largest such prime to have non-decreasing digits. [Hasler]

+ 2347 and 4723 are the only primes concatenated from two double-digit primes whose the products of digits are perfect numbers, i.e., 6, 28. [Loungrides]

+ The leading digits of the googol-th prime number. [Schmidt]

(There is one curio for this number that has not yet been approved by an editor.)

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