Prime

The set of all prime numbers.

Example

Prime .each (100) do |prime|
 p prime #=> 2, 3, 5, 7, 11, ...., 97
end

Prime is Enumerable:

Prime .first 5 # => [2, 3, 5, 7, 11]

Retrieving the instance

For convenience, each instance method of Prime .instance can be accessed as a class method of Prime .

e.g.

Prime .instance .prime? (2) #=> true
Prime .prime? (2) #=> true

Generators

A "generator" provides an implementation of enumerating pseudo-prime numbers and it remembers the position of enumeration and upper bound. Furthermore, it is an external iterator of prime enumeration which is compatible with an Enumerator.

Prime::PseudoPrimeGenerator is the base class for generators. There are few implementations of generator.

Prime::EratosthenesGenerator

Uses eratosthenes’ sieve.

Prime::TrialDivisionGenerator

Uses the trial division method.

Prime::Generator23

Generates all positive integers which are not divisible by either 2 or 3. This sequence is very bad as a pseudo-prime sequence. But this is faster and uses much less memory than the other generators. So, it is suitable for factorizing an integer which is not large but has many prime factors. e.g. for Prime#prime? .

1Note

class Fixnum
def prime?
 ('1' * self) !~ /^1?$|^(11+?)\1円+$/
end
end
10.prime?

Related methods