How to create the most compact mapping n → isprime(n) up to a limit N?

Question

Naturally, for bool isprime(number) there would be a data structure I could query.
I define the best algorithm, to be the algorithm that pr

Answer 1

Python 3:

def is_prime(a):
    return a > 1 and all(a % i for i in range(2, int(a**0.5) + 1))