Project Euler > Problem 129 > Repunit divisibility (Java Solution)


A number consisting entirely of ones is called a repunit. We shall define R(k) to be a repunit of length k; for example, R(6) = 111111.

Given that n is a positive integer and GCD(n, 10) = 1, it can be shown that there always exists a value, k, for which R(k) is divisible by n, and let A(n) be the least such value of k; for example, A(7) = 6 and A(41) = 5.

The least value of n for which A(n) first exceeds ten is 17.

Find the least value of n for which A(n) first exceeds one-million.



The solution may include methods that will be found here: .

public interface EulerSolution{

public String run();

* Solution to Project Euler problem 29
* By Nayuki Minase

import java.math.BigInteger;
import java.util.HashSet;
import java.util.Set;

public final class p029 implements EulerSolution {

public static void main(String[] args) {
System.out.println(new p029().run());

public String run() {
Set<BigInteger> generated = new HashSet<BigInteger>();
for (int a = 2; a <= 100; a++) {
for (int b = 2; b <= 100; b++)
return Integer.toString(generated.size());


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