extras: add P16-P23, P25

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

P22.java

@@ -0,0 +1,25 @@
+import java.util.Scanner;
+
+public class P22 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        System.out.print("Enter an integer: ");
+        int n = scanner.nextInt();
+
+        System.out.println(n + " is " + (prime(n) ? "" : "not ") + "a prime number.");
+
+        scanner.close();
+    }
+
+    public static boolean prime(int number) {
+        if (number <= 1)
+            return false;
+
+        for (int i = 2; i <= Math.sqrt(number); i++)
+            if (number % i == 0)
+                return false;
+
+        return true;
+    }
+}