diff --git a/project_euler/problem_06/sol1.py b/project_euler/problem_06/sol1.py
index d6506ea28..38f995bbf 100644
--- a/project_euler/problem_06/sol1.py
+++ b/project_euler/problem_06/sol1.py
@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@ numbers and the square of the sum.
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,6 +27,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_of_squares = 0
     sum_of_ints = 0
diff --git a/project_euler/problem_06/sol2.py b/project_euler/problem_06/sol2.py
index 5032775f9..f4d74c993 100644
--- a/project_euler/problem_06/sol2.py
+++ b/project_euler/problem_06/sol2.py
@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@ numbers and the square of the sum.
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,6 +27,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_cubes = (n * (n + 1) // 2) ** 2
     sum_squares = n * (n + 1) * (2 * n + 1) // 6
diff --git a/project_euler/problem_06/sol3.py b/project_euler/problem_06/sol3.py
index 385ad0515..8b5c5d3ba 100644
--- a/project_euler/problem_06/sol3.py
+++ b/project_euler/problem_06/sol3.py
@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -16,7 +16,7 @@ numbers and the square of the sum.
 import math
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -28,6 +28,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_of_squares = sum([i * i for i in range(1, n + 1)])
     square_of_sum = int(math.pow(sum(range(1, n + 1)), 2))
diff --git a/project_euler/problem_06/sol4.py b/project_euler/problem_06/sol4.py
index 912a3e8f6..5fae84008 100644
--- a/project_euler/problem_06/sol4.py
+++ b/project_euler/problem_06/sol4.py
@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@ numbers and the square of the sum.
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,7 +27,7 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
-    >>> solution(100)
+    >>> solution()
     25164150
     """
     sum_of_squares = n * (n + 1) * (2 * n + 1) / 6
diff --git a/project_euler/problem_06/test_solutions.py b/project_euler/problem_06/test_solutions.py
deleted file mode 100644
index 6d5337789..000000000
--- a/project_euler/problem_06/test_solutions.py
+++ /dev/null
@@ -1,18 +0,0 @@
-from .sol1 import solution as sol1
-from .sol2 import solution as sol2
-from .sol3 import solution as sol3
-from .sol4 import solution as sol4
-
-
-def test_solutions() -> None:
-    """
-    >>> test_solutions()
-    """
-    assert sol1(10) == sol2(10) == sol3(10) == sol4(10) == 2640
-    assert sol1(15) == sol2(15) == sol3(15) == sol4(15) == 13160
-    assert sol1(20) == sol2(20) == sol3(20) == sol4(20) == 41230
-    assert sol1(50) == sol2(50) == sol3(50) == sol4(50) == 1582700
-
-
-if __name__ == "__main__":
-    test_solutions()