diff --git a/backtracking/knight_tour.py b/backtracking/knight_tour.py
index 7d1e03b83..e4a93fbc2 100644
--- a/backtracking/knight_tour.py
+++ b/backtracking/knight_tour.py
@@ -4,12 +4,12 @@ from typing import List, Tuple
 
 
 def get_valid_pos(position: Tuple[int], n: int) -> List[Tuple[int]]:
-    '''
+    """
     Find all the valid positions a knight can move to from the current position.
 
     >>> get_valid_pos((1, 3), 4)
     [(2, 1), (0, 1), (3, 2)]
-    '''
+    """
 
     y, x = position
     positions = [
@@ -20,7 +20,7 @@ def get_valid_pos(position: Tuple[int], n: int) -> List[Tuple[int]]:
         (y + 2, x + 1),
         (y + 2, x - 1),
         (y - 2, x + 1),
-        (y - 2, x - 1)
+        (y - 2, x - 1),
     ]
     permissible_positions = []
 
@@ -33,7 +33,7 @@ def get_valid_pos(position: Tuple[int], n: int) -> List[Tuple[int]]:
 
 
 def is_complete(board: List[List[int]]) -> bool:
-    '''
+    """
     Check if the board (matrix) has been completely filled with non-zero values.
 
     >>> is_complete([[1]])
@@ -41,15 +41,15 @@ def is_complete(board: List[List[int]]) -> bool:
 
     >>> is_complete([[1, 2], [3, 0]])
     False
-    '''
+    """
 
     return not any(elem == 0 for row in board for elem in row)
 
 
 def open_knight_tour_helper(board: List[List[int]], pos: Tuple[int], curr: int) -> bool:
-    '''
+    """
     Helper function to solve knight tour problem.
-    '''
+    """
 
     if is_complete(board):
         return True
@@ -67,7 +67,7 @@ def open_knight_tour_helper(board: List[List[int]], pos: Tuple[int], curr: int)
 
 
 def open_knight_tour(n: int) -> List[List[int]]:
-    '''
+    """
     Find the solution for the knight tour problem for a board of size n. Raises
     ValueError if the tour cannot be performed for the given size.
 
@@ -78,7 +78,7 @@ def open_knight_tour(n: int) -> List[List[int]]:
     Traceback (most recent call last):
     ...
     ValueError: Open Kight Tour cannot be performed on a board of size 2
-    '''
+    """
 
     board = [[0 for i in range(n)] for j in range(n)]
 
diff --git a/dynamic_programming/max_non_adjacent_sum.py b/dynamic_programming/max_non_adjacent_sum.py
index 1d771f21f..b9f99a226 100644
--- a/dynamic_programming/max_non_adjacent_sum.py
+++ b/dynamic_programming/max_non_adjacent_sum.py
@@ -4,7 +4,7 @@ from typing import List
 
 
 def maximum_non_adjacent_sum(nums: List[int]) -> int:
-    '''
+    """
     Find the maximum non-adjacent sum of the integers in the nums input list
 
     >>> print(maximum_non_adjacent_sum([1, 2, 3]))
@@ -15,14 +15,15 @@ def maximum_non_adjacent_sum(nums: List[int]) -> int:
     0
     >>> maximum_non_adjacent_sum([499, 500, -3, -7, -2, -2, -6])
     500
-    '''
+    """
     if not nums:
         return 0
     max_including = nums[0]
     max_excluding = 0
     for num in nums[1:]:
         max_including, max_excluding = (
-            max_excluding + num, max(max_including, max_excluding)
+            max_excluding + num,
+            max(max_including, max_excluding),
         )
     return max(max_excluding, max_including)
 
diff --git a/project_euler/problem_551/sol1.py b/project_euler/problem_551/sol1.py
index bbdd4d6b0..817474b35 100644
--- a/project_euler/problem_551/sol1.py
+++ b/project_euler/problem_551/sol1.py
@@ -40,12 +40,8 @@ def next_term(a_i, k, i, n):
     ending term is a_10=62, then (61, 9) is returned.
     """
     # ds_b - digitsum(b)
-    ds_b = 0
-    for j in range(k, len(a_i)):
-        ds_b += a_i[j]
-    c = 0
-    for j in range(min(len(a_i), k)):
-        c += a_i[j] * base[j]
+    ds_b = sum(a_i[j] for j in range(k, len(a_i)))
+    c = sum(a_i[j] * base[j] for j in range(min(len(a_i), k)))
 
     diff, dn = 0, 0
     max_dn = n - i