101

This number is a prime.

Just showing those entries submitted by 'Firoozbakht': (Click here to show all)

101^101-100^100+99^99-98^98+...-2^2+1^1 is prime. Note that 101 is the only known odd prime p, such that p^p-(p-1)^(p-1)+...-2^2+1^1 is prime. [Firoozbakht]

The only known prime p such that sigma(p-1) = sigma(p+1) + 1. [Firoozbakht]