7224444666666888888889

This number is a prime.

                                                    72 2444466666 6888888889

The only prime formed by inserting in ascending order, between the digits of a double-digit number n, the concatenation of the even digits d, d times each of them, (n=79), i.e., zero 0’s, two 2’s, four 4’s six 6’s and eight 8’s. [Loungrides]