Math Fact: Known by few

1. 73939133 is the largest known prime number that, if you keep removing digits from the right, will always leave a prime number
2. If you write these numbers on a calculator and turn it upside down :

• 5318008, which when turned over spells "BOOBIES". 
•  0.7734, which becomes "hELLO".
•  5304577351 spells "I SELL ShOES."    

     3.  Among all shapes with the same area circle has the shortest perimeter