add Euler's Totient Function

algorithms/Python/number_theory/Eulers_Totient_Function.py

@@ -0,0 +1,23 @@
+# counts the positive integers up to a given integer n that are relatively prime to n
+
+def euler_totient(n):
+    result = n
+    p = 2
+
+    while p * p <= n:
+        if n % p == 0:
+            while n % p == 0:
+                n //= p
+            result *= (1.0 - (1.0 / float(p)))
+        p += 1
+
+    if n > 1:
+        result *= (1.0 - (1.0 / float(n)))
+
+    return int(result)
+# TIME COMPLEXITY - O(sqrt(N))
+
+# Example usage
+#number = 10 ———> 4
+
+