946
This number is a composite.
946 is the only three-digit number m such that the reversal of concatenation of the first m natural numbers is prime. [Firoozbakht]
The largest known number n such that n is the sum of two consecutive primes but not the sum of two sums of two consecutive primes. [Capelle]
(There are 3 curios for this number that have not yet been approved by an editor.)
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