Factorial primes: Difference between revisions

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~~Takes~~ about 32 seconds to find the first 33 factorial primes on my machine (Ryzen 5 1500X).

This takes about 32 seconds to find the first 33 factorial primes on my machine (Ryzen 5 1500X).

from itertools import count

from itertools import islice

from typing import Iterable

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def factorials() -> Iterable[int]:

~~i: int~~ = 1

fact = 1

n: ~~int~~ = 1

for i in count(1):

~~while~~ ~~True:~~

yield fact

~~yield~~ n

fact *= i

n *= i

i += 1

def factorial_primes() -> Iterable[Tuple[int, int, str]]:

for i, n in enumerate(factorials()):

for n, fact in enumerate(factorials()):

if gmpy2.is_prime(n - 1):

if gmpy2.is_prime(fact - 1):

yield (i, n - 1, "-")

yield (n, fact - 1, "-")

if gmpy2.is_prime(n + 1):

if gmpy2.is_prime(fact + 1):

yield (i, n + 1, "+")

yield (n, fact + 1, "+")

def ~~main~~(n=10) -> None:

def print_factorial_primes(limit=10) -> None:

print(f"First {n} factorial primes.")

print(f"First {limit} factorial primes.")

for i, ~~factorial_prime~~, op in islice(factorial_primes(), 1, n + 1):

for n, fact_prime, op in islice(factorial_primes(), 1, limit + 1):

s = str(~~factorial_prime~~)

s = str(fact_prime)

if len(s) > 40:

s = f"{s[:20]}...{s[-20:]} ({len(s)} digits)"

print(f"{i}! {op} 1 = {s}")

print(f"{n}! {op} 1 = {s}")

if __name__ == "__main__":

import sys

~~main~~(int(sys.argv[1]) if len(sys.argv) > 1 else 10)

print_factorial_primes(int(sys.argv[1]) if len(sys.argv) > 1 else 10)

</syntaxhighlight>