10000...00001 (127-digits)

This number is a prime.

              1000000 0000000000 0000000000 0000000000 0000000000 0000000000
0000008000 0000000000 0000000000 0000000000 0000000000 0000000000 0000000001

A tetradic prime of the form 100^n+8*10^n+1 containing a Mersenne prime number of digits. [Michel]