is_prime

Is the given number a prime number?

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require "is_prime"

3.prime? # => true
4.prime? # => false

The implementation is just one line.

('1' * N) !~ /^1?$|^(11+?)\1+$/

Read more about it here.

[sudo] gem install is_prime

is_prime is tested in Mac OS X 10.6.6, 10.6.7 using Ruby 1.8.7, 1.9.2.

is_prime is released under the MIT license.