Check if a number is Primorial Prime or not in Python

Suppose we have a number n, we have to check whether n is a primorial prime or not. A number is said to be a primorial prime when it is a prime number of the form pN# + 1 or pN# – 1 , where pN# indicates the primorial of pN such that the product of first N prime numbers.

So, if the input is like 29, then the output will be True as 29 is Primorial prime of the form pN - 1 if N=3, Primorial is 2*3*5 = 30 and 30-1 = 29.

To solve this, we will follow these steps −

• MAX := 100000
• prime := A list of size MAX and fill with True
• arr := a new list
• Define a function SieveOfEratosthenes() . This will take
• for pri in range 2 to int(square root of (MAX)) + 1, do
  • if prime[pri] is same as True, then
    • for i in range pri * 2 to MAX, update in each step by pri, do
      • prime[i] := False
• for pri in range 2 to MAX, do
  • if prime[pri] is non-zero, then
    • insert pri at the end of arr
• From the main method, do the following −
• if prime[n] is zero, then
  • return False
• product := 1, i := 0
• while product < n, do
  • product := product * arr[i]
  • if product + 1 is same as n or product - 1 is same as n, then
    • return True
  • i := i + 1
• return False

Example

Let us see the following implementation to get better understanding −

 Live Demo

from math import sqrt MAX = 100000 prime = [True] * MAX arr = [] def SieveOfEratosthenes() :    for pri in range(2, int(sqrt(MAX)) + 1) :       if prime[pri] == True :          for i in range(pri * 2 , MAX, pri) :             prime[i] = False    for pri in range(2, MAX) :       if prime[pri] :          arr.append(pri) def check_primorial_prime(n) :    if not prime[n] :       return False    product, i = 1, 0    while product < n :       product *= arr[i]       if product + 1 == n or product - 1 == n :          return True       i += 1    return False SieveOfEratosthenes() n = 29 print(check_primorial_prime(n))

Input

29

Output

True