Amazing Number Facts No

No 18

7 is a prime number
73 is a prime number
739 is a prime number
7393 is a prime number
73939 is a prime number
739391 is a prime number
7393913 is a prime number
73939133 is a prime number
73939133 is an amazing prime number...
...if you keep chopping the end digit off you still get a prime.
It is the largest known prime with this property.
What's the largest one you can find in The List? If you have answers, discoveries, new questions etc to do with this Number Fact then...
E-mail us at madrascollege.maths@fife.gov.uk
...and we will publish them here.