primecount is a command-line program that counts the primes below an integer x ≤ 10^31 using highly optimized implementations of the combinatorial prime counting algorithms.
v8.5BSD 2-Clause
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Primesieve
Primesieve.Primesieve
primesieve is a command-line program that generates primes using the sieve of Eratosthenes algorithm. It can generate primes and prime k-tuplets (twin primes, prime triplets, ...) up to 2^64 and find the nth prime.