11111...11111 (127-digits)

This number is a composite.

              1111111 1111111111 1111111111 1111111111 1111111111 1111111111
1111111111 1111111111 1111111111 1111111111 1111111111 1111111111 1111111111

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

A repunit hex-congruent prime in bases 5 and 6. [Dobb]