7639

This number is a prime.

The largest 4-digit prime formed by inserting between the digits of a double-digit prime (emirp) the product of its digits. Note that its reversal is a 2-sphenic number, i.e., 9367 = 17 × 19 × 29, whose the concatenation in order of prime factors, i.e., 171929, is an emirp. [Loungrides]