In mathematical parlance, the prime number 113 is said to be permutable because it remains prime regardless of how the digits are arranged, that is 131 and 311.
Another example of this is 199, which stays prime at 919 and 991.
The first question this week is which three-digit prime number - that does not contain the digit 1 - remains prime when rearranged to form two other numbers?
If you get that solved quickly, try this much harder question as a bonus problem:
This eleven-digit number looks likely to be prime, but actually it has just two factors. Can you find out what they are?
This was first published in October 2008