42

This number is a composite.

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

42 = (π(4)*π(2)) * (prime(4)*prime(2)). Note that 42 is the only number less than 20000000 with this property. [Firoozbakht]

42^42 + π(42) is prime. It is interesting that all numbers less than 42 with this property are are all prime factors of 42. [Firoozbakht]

All five numbers 1 + 42, 1 + 4242, 1 + 424242, 1 + 42424242 and 1 + 4242424242 are prime. [Firoozbakht]