from math import sqrt

#Same but with some memoization, better if you need to check some numbers more than once
def prime(x, cache={}): 
    if x not in cache:
        if x <= 1:
            cache[x]= False
            return False
        for i in range(2,int(sqrt(x))):
            if x % i is 0:
                cache[x] = False
                return False
        cache[x] = True        
    return cache[x]