data/problems/346.yml
---
:id: 346
:name: Strong Repunits
:url: https://projecteuler.net/problem=346
:content: "The number 7 is special, because 7 is 111 written in base 2, and 11 written
in base 6 \n(i.e. 7<sub>10</sub> = 11<sub>6</sub> = 111<sub>2</sub>). In other
words, 7 is a repunit in at least two bases b \\> 1.\n\nWe 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}. \nFurthermore, the sum of all
strong repunits below 1000 equals 15864.\n\nFind the sum of all strong repunits
below 10<sup>12</sup>.\n"