Sieve of Eratosthenes

input_to_int = max(1, int(input_to)) markers = [False for _ in range(input_to_int+1)] markers[0] = True markers[1] = True for (index, marker) in enumerate(markers): if markers[index]: continue for n in range(index * 2, len(markers), index): markers[n] = True [n for n, marker in enumerate(markers) if not marker]