971

971 is a prime number.

971 is the largest prime containing only odd digits, in decreasing order.

971 is the largest prime formed from the concatenation of a one-digit composite number, one-digit prime number, and one-digit number that is neither prime nor composite.

971, 719, and 197 are all primes.

971 is the smallest of three consecutive primes with a difference of six; a prime p such that p (971), p + 6 (977), and p + 12 (983) are all primes (A047948).

Source: Prime Curios!