# Problem 346: Strong Repunits
The number 7 is special, because 7 is 111 written in base 2, and 11
written in base 6 (i.e. 710 = 116 = 1112). In other words, 7 is a
repunit in at least two bases b > 1. We shall call a positive integer
with this property a strong repunit. It can be verified that there are 8
strong repunits below 50: {1,7,13,15,21,31,40,43}. Furthermore, the sum
of all strong repunits below 1000 equals 15864. Find the sum of all
strong repunits below 1012.