diff --git a/mathtools.py b/mathtools.py
index 58081fa..e42cf0d 100644
--- a/mathtools.py
+++ b/mathtools.py
@@ -10,3 +10,35 @@ def isPrime(n):
         if n % i == 0:
             return False
     return True
+
+def factorial(n):
+    '''Returns the factorial of a number'''
+    if n == 0:
+        return 1
+    else:
+        return n * factorial(n-1)
+
+def arithmetic(a, difference, n):
+    '''Calculates the sum of a arithmetic serie of n elements.
+       An arithmetic sequence is of the form: a, a+d, a+2d, a+3d,...
+       n is the number of elements in the sequence.'''
+    #Get the arithmetic sequence
+    sequence = [a+difference*x for x in range(n)]
+    #Calculates its sum
+    return sum(sequence)
+
+def fib(n):
+    ''' Calculates the n value of the fibonacci sequence'''
+    if n == 0:
+        return 0
+    elif n == 1:
+        return 1
+    else:
+        return fib(n-1)+fib(n-2)
+
+def geometric(a, ratio, n):
+    '''Calculates the sum of a geometric serie of n elements.
+       A geometric sequence is of the form: a, a*r, a*r*r, a*r*r*r,...
+       n is the number of elements in the sequence.'''
+    #Use the sum formula:
+    return a*(1-ratio**n)/(1-ratio)