From 5ac2a0a8ad6708bde4b3f5477626bc911c4baf1f Mon Sep 17 00:00:00 2001
From: Hatter Jiang <jht5945@gmail.com>
Date: Fri, 18 Jul 2025 00:00:00 +0800
Subject: [PATCH] feat: add phi

---
 src/main/java/me/hatter/math/Phi.java | 28 +++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 src/main/java/me/hatter/math/Phi.java

diff --git a/src/main/java/me/hatter/math/Phi.java b/src/main/java/me/hatter/math/Phi.java
new file mode 100644
index 0000000..66dcbf1
--- /dev/null
+++ b/src/main/java/me/hatter/math/Phi.java
@@ -0,0 +1,28 @@
+package me.hatter.math;
+
+import java.math.BigInteger;
+
+public class Phi {
+
+    public static void main(String[] args) {
+        for (long x = 4; x < 10000; x++) {
+            // gcd(3, x) = 1
+            if (BigInteger.valueOf(3).gcd(BigInteger.valueOf(x)).equals(BigInteger.ONE)) {
+                // 3 ^ phi(x) mod x = 1
+                System.out.println(BigInteger.valueOf(3).modPow(phi(BigInteger.valueOf(x)), BigInteger.valueOf(x)));
+            }
+        }
+    }
+
+    public static BigInteger phi(BigInteger n) {
+        BigInteger p = BigInteger.valueOf(0);
+        BigInteger i = BigInteger.valueOf(1);
+        while (i.compareTo(n) < 0) {
+            if (i.gcd(n).equals(BigInteger.ONE)) {
+                p = p.add(BigInteger.ONE);
+            }
+            i = i.add(BigInteger.ONE);
+        }
+        return p;
+    }
+}