1111111111111

This number is a composite.

                                                              111 1111111111

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

            1
         1 1 1 1
          1 1 1
         1 1 1 1
            1

A star-congruent prime of order 2 in bases 2 and 5. [Dobb]