172

This number is a composite.

Seventeen 2's followed by two 17's is prime. [De Geest]

172 = π(1+7+2) * prime(1*7*2). It is the only known number (up to 10^8) with this property. [Firoozbakht]

172 = phi(1+7+2) * prime(1*7*2). It is the only known number (up to 10^8) with this property. [Firoozbakht]

There is a prime gap of 172 between the primes 140737488355609 and 140737488355781. This is the largest gap in the range [140737488353699, 140737488356209]. The first integer in this interval is the lesser element in a twin prime pair which was the largest known in 1975 while the last integer in this interval is the greater element in the next twin prime pair. [Schiffman]