update from Atlas

operator/factorial/SimpleFactorial.java

@@ -0,0 +1,43 @@
+class SimpleFactorial {
+
+    public static long factorial(long n) {
+        return n < 2 ? 1 : n * factorial(n-1);
+    }
+
+    public static void main(String args[]) {
+        for (long i = 1; i <= 25; i++) {
+            System.out.println(i + "! = " + factorial(i));
+
+        }
+    }
+}
+
+/* output: ncorrect results starting with 21!
+
+1! = 1
+2! = 2
+3! = 6
+4! = 24
+5! = 120
+6! = 720
+7! = 5040
+8! = 40320
+9! = 362880
+10! = 3628800
+11! = 39916800
+12! = 479001600
+13! = 6227020800
+14! = 87178291200
+15! = 1307674368000
+16! = 20922789888000
+17! = 355687428096000
+18! = 6402373705728000
+19! = 121645100408832000
+20! = 2432902008176640000
+21! = -4249290049419214848
+22! = -1250660718674968576
+23! = 8128291617894825984
+24! = -7835185981329244160
+25! = 7034535277573963776
+
+*/