Coderbyte Python Challenge: PentagonalNumber

PentagonalNumber.py

# PentagonalNumber(num) reads num which will be a positive integer and determine how many dots exist in a pentagonal shape 
# around a center dot on the Nth iteration. 

# For example, in the image below you can see that on the first iteration there is only a single dot, 
# on the second iteration there are 6 dots, on the third there are 16 dots, and on the fourth there are 31 dots. 

# The formula for this sequence is (5(n-1)^2 + 5(n-1) + 2) / 2

def PentagonalNumber(num): 
    num = num - 1
    number = ((5*(num**2)) + (5*num) + 2) / 2 
    return number
    
# keep this function call here  
print(PentagonalNumber(input()))