61

This number is a prime.

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

(2⁶¹ - 1)/(2 - 1) and (2⁶¹ + 1)/(2 + 1) are both primes. [Luhn]

61 is the only known example where the reversal of a Mersenne prime exponent gives a power of 2. [Luhn]

(61+1)^61-61 is prime. [Luhn]