diff --git a/DIRECTORY.md b/DIRECTORY.md
index 90fec52..a01b826 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -21,6 +21,7 @@
 ## Projecteuler
   * [Problem1](./ProjectEuler/Problem1.php)
   * [Problem2](./ProjectEuler/Problem2.php)
+  * [Problem3](./ProjectEuler/Problem3.php)
   * [Problem5](./ProjectEuler/Problem5.php)
   * [Problem7](./ProjectEuler/Problem7.php)
   * [Problem9](./ProjectEuler/Problem9.php)
diff --git a/ProjectEuler/Problem3.php b/ProjectEuler/Problem3.php
new file mode 100644
index 0000000..dd8843f
--- /dev/null
+++ b/ProjectEuler/Problem3.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * Problem:
+ *
+ * The prime factors of 13195 are 5, 7, 13 and 29.
+ *
+ * What is the largest prime factor of the number 600851475143?
+ *
+ *
+ * Answer:
+ *
+ * 6857
+ *
+ *
+ * @link https://projecteuler.net/problem=3
+ */
+function problem3(): int
+{
+    $n = 600851475143;
+    $i = 2;
+    while ($i * $i < $n) {
+        while ($n % $i == 0) {
+            $n /= $i;
+        }
+        $i++;
+    }
+
+    return $n;
+}
diff --git a/tests/ProjectEulerTest.php b/tests/ProjectEulerTest.php
index 75d366a..e930026 100644
--- a/tests/ProjectEulerTest.php
+++ b/tests/ProjectEulerTest.php
@@ -5,6 +5,7 @@ use PHPUnit\Framework\TestCase;
 require_once __DIR__.'/../vendor/autoload.php';
 require_once __DIR__.'/../ProjectEuler/Problem1.php';
 require_once __DIR__.'/../ProjectEuler/Problem2.php';
+require_once __DIR__.'/../ProjectEuler/Problem3.php';
 require_once __DIR__.'/../ProjectEuler/Problem5.php';
 require_once __DIR__.'/../ProjectEuler/Problem7.php';
 require_once __DIR__.'/../ProjectEuler/Problem9.php';
@@ -22,6 +23,11 @@ class ProjectEulerTest extends TestCase
         $this->assertSame(4613732, problem2());
     }
 
+    public function testProblem3(): void
+    {
+        $this->assertSame(6857, problem3());
+    }
+
     public function testProblem5(): void
     {
         $this->assertSame(232792560, problem5());