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Oct 20, 2017 · Both return either True or False. Function isPrime1 is very fast to return False is a number is not a prime. For example with a big number. But it is slow in testing True for big prime numbers. Function isPrime2 is faster in returning True for prime numbers. But if a number is big and it is not prime, it takes too long to return a value.
Nov 11, 2012 · SymPy is one choice. It is a Python library for symbolic mathematics. It provides several functions for prime. isprime(n) # Test if n is a prime number (True) or not (False). primerange(a, b) # Generate a list of all prime numbers in the range [a, b). randprime(a, b) # Return a random prime number in the range [a, b). primepi(n) # Return the ...
Jun 12, 2019 · Check Prime Number, in python. logic confusion. 0. Validate if input number is prime. 0. How to properly ...
using your code, and focusing on code structure: def is_prime(x): # function contents must be indented if x == 0: return False elif x == 1: return False # your base cases need to check X, not n, and move them out of the loop elif x == 2: return True for n in range(3, x-1): if x % n == 0: return False # only return true once you've checked ALL the numbers(for loop done) return True
Feb 14, 2016 · The else statement that you put inside the for loop means that if that number(num) is divisible by this current no represented by i, return true considering it as a prime which IS NOT CORRECT. Suggestion. Your outer loop starts with 1 which should change to 2, as 1 is not a prime number. Solution
Mar 8, 2013 · Will not work if n is 0 or 1' # Make sure n is a positive integer n = abs(int(n)) # Case 1: the number is 2 (prime) if n == 2: return True # Case 2: the number is even (not prime) if n % 2 == 0: return False # Case 3: the number is odd (could be prime or not) # Check odd numbers less than the square root for possible factors r = math.sqrt(n) x ...
If you are absolutely set on using a trial division based method, I would recommend you multiply a large number of small primes and store the resulting composite number. Then you can take the Greatest Common Divisor (GCD) using a standard algorithm (such as 'fraction.gcd'). If the answer is not 1, then the number tested is definitely not prime.
May 30, 2020 · When testing if X is prime, the algorithm doesn't have to check every number up to the square root of X, it only has to check the prime numbers up to the sqrt(X). Thus, it can be more efficient if it refers to the list of prime numbers as it is creating it.
You can use Miller-Rabin primality test to check whether a number is prime or not. You can find its Python implementations here. Always use timeit module to time your code, the 2nd one takes just 15us:
Nov 11, 2018 · Here's a Python implementation of a well-known algorithm (the Sieve of Eratosthenes) for generating the first n primes (credit to tech.io for the code): def sieve(n): primes = 2*[False] + (n-1)*[True] for i in range(2, int(n**0.5+1.5)): for j in range(i*i, n+1, i): primes[j] = False.
