7777557757577557777

This number is a prime.

                                                        777755775 7577557777

Just showing those entries submitted by 'Marcel': (Click here to show all)

The only hexagon-congruent prime of order 3 whose the ring is an alternate number:

     7 7 7 
    7 5 5 7 
   7 5 7 5 7 
    7 5 5 7 
     7 7 7