diff --git "a/Retos/Reto #21 - N\303\232MEROS PRIMOS GEMELOS [Media]/php/kodenook.php" "b/Retos/Reto #21 - N\303\232MEROS PRIMOS GEMELOS [Media]/php/kodenook.php"
new file mode 100644
index 0000000000..efcee95f7f
--- /dev/null
+++ "b/Retos/Reto #21 - N\303\232MEROS PRIMOS GEMELOS [Media]/php/kodenook.php"	
@@ -0,0 +1,64 @@
+<?php
+
+declare (strict_types = 1);
+
+/**
+ * The function checks if a given number is prime or not.
+ *
+ * @param int num The parameter "num" is an integer that represents the number we want to check if it
+ * is prime or not.
+ *
+ * @return bool a boolean value, either true or false.
+ */
+function isPrime(int $num): bool
+{
+    if ($num <= 1) {
+        return false;
+    }
+
+    for ($i = 2; $i <= (int) sqrt($num); $i++) {
+        if (fmod($num, $i) === 0.0) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+/**
+ * The function "primeTwins" returns a string containing pairs of prime numbers that are two units
+ * apart, up to a given maximum number.
+ *
+ * @param int numMax The parameter `numMax` represents the maximum number up to which we want to find
+ * prime twin pairs.
+ *
+ * @return string a string that contains pairs of prime numbers that are twin primes. Each pair is
+ * enclosed in parentheses and separated by a comma.
+ */
+function primeTwins(int $numMax): string
+{
+    $numbers = [];
+    $response = '';
+
+    for ($i = 0; $i <= $numMax; $i++) {
+        if (isPrime($i)) {
+            array_push($numbers, $i);
+        }
+    }
+
+    for ($i = 0; $i < count($numbers); $i++) {
+        if ($i + 1 >= count($numbers)) {
+            continue;
+        }
+
+        if ($numbers[$i + 1] - $numbers[$i] === 2) {
+            $response .= '(' . $numbers[$i] . ',' . $numbers[$i + 1] . ') ';
+        }
+    }
+
+    return $response;
+}
+
+echo primeTwins(14) . PHP_EOL;
+echo primeTwins(7) . PHP_EOL;
+echo primeTwins(2) . PHP_EOL;