Improve Project Euler problem 012 solution 1 (#5731)

* Improve solution

* Uncomment code that has been commented due to slow execution affecting Travis

* Retest

project_euler/problem_012/sol1.py

@@ -21,17 +21,20 @@ We can see that 28 is the first triangle number to have over five divisors.
 What is the value of the first triangle number to have over five hundred
 divisors?
 """
-from math import sqrt
 
 
 def count_divisors(n):
-    nDivisors = 0
-    for i in range(1, int(sqrt(n)) + 1):
-        if n % i == 0:
-            nDivisors += 2
-    # check if n is perfect square
-    if n ** 0.5 == int(n ** 0.5):
-        nDivisors -= 1
+    nDivisors = 1
+    i = 2
+    while i * i <= n:
+        multiplicity = 0
+        while n % i == 0:
+            n //= i
+            multiplicity += 1
+        nDivisors *= multiplicity + 1
+        i += 1
+    if n > 1:
+        nDivisors *= 2
     return nDivisors
 
 
@@ -39,9 +42,8 @@ def solution():
     """Returns the value of the first triangle number to have over five hundred
     divisors.
 
-    # The code below has been commented due to slow execution affecting Travis.
-    # >>> solution()
-    # 76576500
+    >>> solution()
+    76576500
     """
     tNum = 1
     i = 1