9767

This number is a prime.

The largest 4-digit prime that can be formed by the concatenation of two 2-digit primes (97 and 67). [Sladcik]

(9767, 9769) is the first case of a twin prime pair that can be represented as the product of a repdigit number and all its truncations minus 1 and plus 1, i.e., 222*22*2-1=9767 and 222*22*2+1=9769. [Loungrides]