Groups
Category
Level
Euler's Totient Function ฯ(n) counts how many integers from 1 to n are coprime with n.
Eulerโs Theorem says that if a and n are coprime, then a raised to the power ฯ(n) is congruent to 1 modulo n.
Prime factorization expresses any integer greater than 1 as a product of primes raised to powers, uniquely up to ordering.
The Sieve of Eratosthenes marks multiples of each prime to find all primes up to n in O(n log log n) time.