Everyone

Alchemy

Eclair

A richly featured app for everything involving prime numbers.

Available utilities: 

-Test numbers for primality.

-Calculate a number's unique prime factorization.

-List every divisor of a number.

-Generate a random prime, with the option to specify a range in which the prime is to be found.

-Browse through a complete list of the first 10,000 primes.

-Calculate pi(n), the prime counting function. This is the number of primes less than or equal to n.

-Calculate the greatest common divisor (GCD) of two numbers.

-Calculate the lowest common multiple (LCM) of two numbers.

-Find the value of Euler's totient function, phi(n). This is the number of positive integers less than or equal to n that are coprime to n.

Most features allow testing of numbers up to 9,999,999,999,999,999 (10^16 -1).

This app is completely free and is not ad supported.

Prime Factory

Prime Factory的最新版本