500
This number is a composite.
The first sum of gaps between consecutive primes that is divisible by one hundred (2 (0) 3 (1) 5 (1) 7 (3) 11 ... 599 (1) 601 (5) 607 (5) 613 = 500). [Fentsor]
The number 500 + 3^3^3^3^3^3^3 is prime. [Patterson]
There are exactly 500 prime numbers between 20000 and 25000 [Bopardikar]
(There is one curio for this number that has not yet been approved by an editor.)
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