85

This number is a composite.

(85¹¹ - 85)/11 ± 1 are twin primes. [Luhn]

Between 641 and 114689 (the second smallest Fermat divisor) there exist 85 prime numbers that could conceivably be Fermat divisors.

There are 85 five-digit primes that begin with 85. [Bopardikar]

The only composite number resulting from the sum of three double-digit consecutive emirps, 17, 31, 37. Note that the ordered concatenation of these emirps, i.e., 173137 is prime. [Loungrides]

The only known Smith number n such that the aliquot sum of n = π(n). [Gupta]