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:
11,111,111,111
This eleven-digit number looks likely to be prime, but actually
it has just two factors. Can you find out what they are?
Find the solution online>>
