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Contents
# coding: utf-8
class Integer
# Algorithm derived from Formulas for pi(n) and the n-th prime by Sebastian
# Martin Ruiz and Jonathan Sondow [arXiv:math/0210312v2 [math.NT]]
# Returns the number of primes equal to or less than self
def π
x = self
return 0 if x == 1
@prime_count ||= ([2] + (3..x).select(&:odd?)).map do |j|
1 + ( ((2 - j.τ)/j).floor ).floor
end.reduce(:+)
end
alias :prime_pi :π
alias :prime_count :π
end
Version data entries
15 entries across 15 versions & 1 rubygems