20

This number is a composite.

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

Reversal(1^20 + 2^20 + ... + 20^20) is prime. Reversal(20) is the only other known number with this property. [Firoozbakht]

20^20 - 11...1 (20 ones) and 20 + 11...1 (20 ones) are primes. [Firoozbakht]