MathDB

N4

Part of 2018 Costa Rica - Final Round

Problems(1)

d is prime if prime p = 10^{d -1} + 10^{d-2} + ...+ 10 + 1

Source: OLCOMA Costa Rica National Olympiad, Final Round, 2018 Shortlist N4

10/1/2021
Let pp be a prime number such that p=10d−1+10d−2+...+10+1p = 10^{d -1} + 10^{d-2} + ...+ 10 + 1. Show that dd is a prime.
primenumber theory