253

This number is a composite.

+ 253 - 1 is the largest prime that the prime number tester on this site will test. [Dunn]

+ 2^5-3 is prime. [Dunn]

+ The smallest value of A(3,k) which is not a prime or prime power. A(m,n) is Ackerman's function. [Hartley]

(There are 4 curios for this number that have not yet been approved by an editor.)

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