137438953481

This number is a prime.

                                                               13 7438953481

+ Bertrand's postulate implies that there are infinitely many numbers a for which floor(2a), floor(22a), floor(222a), ... are all prime. The smallest of these is a = 1.25164 75977 90463 01759 44320 53623... and generates the Bertrand primes: 2, 5, 37, 137438953481, .... The next Bertrand prime has 41,373,247,571 digits. [Caldwell]

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