Here are solutions for the three bonus problems that appeared in the September/October 2024 Puzzle Corner column we guest edited. Solutions for S/O2, S/O4, and S/O6 are below; those for S/O1, S/O3, and S/O5 can be found here. S/O2. Frank notes that a repunit Rk is a decimal integer consisting of the digit 1 repeated k times, with k > 0. For example, R1 = 1, R2 = 11, R3 = 111, etc. Let N be any integer not divisible by 2 or 5. Prove that there is a repunit…
