diff --git a/maths/addition.py b/maths/addition.py
new file mode 100644
index 0000000..d9b4231
--- /dev/null
+++ b/maths/addition.py
@@ -0,0 +1,16 @@
+def add(first_number, second_number):
+    """
+    >>> add(1, 2)
+    3
+    >>> add(1.1, 2.2)
+    3.3000000000000003
+    >>> add(-1.1, 1.1)
+    0.0
+    """
+    return first_number + second_number
+
+
+if __name__ == "if __name__ == ''":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/count_digits.py b/maths/count_digits.py
new file mode 100644
index 0000000..d4ce2e3
--- /dev/null
+++ b/maths/count_digits.py
@@ -0,0 +1,27 @@
+def count_digits(number: int) -> int:
+    """
+    >>> count_digits(-123)
+    3
+    >>> count_digits(-1)
+    1
+    >>> count_digits(0)
+    1
+    >>> count_digits(123)
+    3
+    >>> count_digits(123456)
+    6
+    """
+    number = abs(number)
+    count = 0
+    while True:
+        number = number // 10
+        count = count + 1
+        if number == 0:
+            break
+    return count
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/count_digits_recursion.py b/maths/count_digits_recursion.py
new file mode 100644
index 0000000..d23bd49
--- /dev/null
+++ b/maths/count_digits_recursion.py
@@ -0,0 +1,21 @@
+def count_digits_recursion(number: int) -> int:
+    """
+    >>> count_digits_recursion(-123)
+    3
+    >>> count_digits_recursion(-1)
+    1
+    >>> count_digits_recursion(0)
+    1
+    >>> count_digits_recursion(123)
+    3
+    >>> count_digits_recursion(123456)
+    6
+    """
+    number = abs(number)
+    return 1 if number < 10 else 1 + count_digits_recursion(number // 10)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/cube_number.py b/maths/cube_number.py
new file mode 100644
index 0000000..b15dc12
--- /dev/null
+++ b/maths/cube_number.py
@@ -0,0 +1,25 @@
+"""
+https://en.wikipedia.org/wiki/Cube_(algebra)
+"""
+
+
+def is_cube_number(number: int) -> bool:
+    """
+    >>> all(is_cube_number(num) for num in [-8, -1, 0, 1, 8, 27, 64, 8000, 216_000])
+    True
+    >>> is_cube_number(4)
+    False
+    >>> is_cube_number(11)
+    False
+    """
+    number = abs(number)
+    for i in range(0, number + 1):
+        if i ** 3 == number:
+            return True
+    return False
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/factorial.py b/maths/factorial.py
new file mode 100644
index 0000000..af8b17e
--- /dev/null
+++ b/maths/factorial.py
@@ -0,0 +1,28 @@
+def factorial(number: int) -> int:
+    """
+    >>> factorial(5)
+    120
+    >>> factorial(0)
+    1
+    >>> import random
+    >>> import math
+    >>> numbers = list(range(0, 50))
+    >>> for num in numbers:
+    ...     assert factorial(num) == math.factorial(num)
+    >>> factorial(-1)
+    Traceback (most recent call last):
+    ...
+    ValueError: factorial() not defined for negative values
+    """
+    if number < 0:
+        raise ValueError("factorial() not defined for negative values")
+    fact = 1
+    for i in range(1, number + 1):
+        fact *= i
+    return fact
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/factorial_recursion.py b/maths/factorial_recursion.py
new file mode 100644
index 0000000..195b7ab
--- /dev/null
+++ b/maths/factorial_recursion.py
@@ -0,0 +1,25 @@
+def factorial_recursion(number: int) -> int:
+    """
+    >>> factorial_recursion(5)
+    120
+    >>> factorial_recursion(0)
+    1
+    >>> import random
+    >>> import math
+    >>> numbers = list(range(0, 50))
+    >>> for num in numbers:
+    ...     assert factorial_recursion(num) == math.factorial(num)
+    >>> factorial_recursion(-1)
+    Traceback (most recent call last):
+    ...
+    ValueError: factorial() not defined for negative values
+    """
+    if number < 0:
+        raise ValueError("factorial() not defined for negative values")
+    return 1 if number == 0 or number == 1 else number * factorial_recursion(number - 1)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
diff --git a/maths/subtract.py b/maths/subtract.py
new file mode 100644
index 0000000..1aafd5b
--- /dev/null
+++ b/maths/subtract.py
@@ -0,0 +1,16 @@
+def subtract(first_number, second_number):
+    """
+    >>> subtract(1.1, 1.1)
+    0.0
+    >>> subtract(10, 5)
+    5
+    >>> subtract(3.14159, 3)
+    0.14158999999999988
+    """
+    return first_number - second_number
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()