Let the digits of our number be* abcd*. Then, we create an 8-digit number by concatenating the digits again:

**abcdabcd**The problem asks us to show that two of the prime factors of

*are 73 and 137.*

**abcdabcd**That's easy because

**73*137 =*

**abcd****10001 =*

**abcd****.**

*abcdabcd*The other prime factors of

**are those prime factors of**

*abcdabcd***.**

*abcd*