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require 'time'
def get_primes7(n)
return [] if n < 2
return [2] if n == 2
# do only odd numbers starting at 3
s = 3.upto(n + 1).select(&:odd?)
mroot = n ** 0.5
half = s.length
i = 0
m = 3
until m > mroot do
if s[i]
j = (m * m - 3) / 2
s[j] = nil
until j >= half do
s[j] = nil
j += m
end
end
i += 1
m = 2 * i + 3
end
[2] + s.compact
end
startTime = Time.now.to_i
periodTime = ENV['RUN_TIME'].to_i
while (Time.now.to_i - startTime) < periodTime do
res = get_primes7(10000000)
puts "Found #{res.length} prime numbers."
end