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TotientPermutation.java
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TotientPermutation.java
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package dev;
import java.util.Arrays;
public class TotientPermutation {
public static void main(String[] args) {
int limit = 10000000; // 10^7
double minRatio = Double.MAX_VALUE;
int result = 0;
for (int n = 2; n < limit; n++) {
int phi = phi(n);
if (isPermutation(n, phi)) {
double ratio = (double) n / phi;
if (ratio < minRatio) {
minRatio = ratio;
result = n;
}
}
}
System.out.println("The value of n is: " + result);
}
// Euler's totient function
public static int phi(int n) {
int result = n;
for (int p = 2; p * p <= n; p++) {
if (n % p == 0) {
while (n % p == 0) {
n /= p;
}
result -= result / p;
}
}
if (n > 1) {
result -= result / n;
}
return result;
}
// Check if two numbers are permutations of each other
public static boolean isPermutation(int a, int b) {
char[] aDigits = String.valueOf(a).toCharArray();
char[] bDigits = String.valueOf(b).toCharArray();
Arrays.sort(aDigits);
Arrays.sort(bDigits);
return Arrays.equals(aDigits, bDigits);
}
}