Solution Exercise 756 : algorithm python to find the largest prim number

Exercise 756

Write a Python algorithm as a function that takes an integer n as argument and returns the largest prime integer less than or equal to n. Example for n = 15, the function returns the largest prime number less than or equal to 15 which is 13.

Solution

# creating function to test if given number is prim or not
def testPrim(m):
    # Initializing number of divisors
    numberDivisors = 0
    
    # while i is divisor of m we increment numberDivisors
    for i in range(1 , m + 1):
        if(m%i == 0):
            numberDivisors = numberDivisors + 1
            
    # a number is prime if and only if it has two divisors, 1 and itself
    if (numberDivisors == 2):
        return True
    else:
        return False
    
def greatestPrim(n):
    # initializing value of searched smallest prim p
    p = n
    while ( not testPrim(p) ):
        p = p - 1
    return p
# Testing algorithm
print("The geatest prim less than or equal 15 is : " , greatestPrim(15))
# The output is : The geatest prim less than or equal 15 is :  13