Adopted new convention from template

src/Python/Problems001-050/Problem021.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python
 """
 Created on 15 Sep 2018
 
@@ -11,9 +11,11 @@ https://projecteuler.net/problem=21
 
 from utils import timeit
 
+
 def sum_divisors(n):
     return sum(i for i in range(1, n // 2 + 1) if n % i == 0)
 
+
 @timeit("Problem 21")
 def compute():
     """
@@ -28,7 +30,8 @@ def compute():
 
     Evaluate the sum of all the amicable numbers under 10000.
     """
-    n = 10000
+
+    n = 10_000
     sum_amicable = 0
     for i in range(1, n):
         value = sum_divisors(i)
@@ -38,5 +41,4 @@ def compute():
 
 
 if __name__ == "__main__":
-
-    print(f"Result for Problem 21: {compute()}")
+    print(f"Result for Problem 21 is {compute()}")