Prime#cosins

prime_cosins.rb

require 'prime'
class Prime
  def cosins n = nil
    return to_enum :cosins, n unless block_given?
    yield [3, 7]
    each(n).each_cons(2) do |p1, p2|
      yield [p1, p2] if p2 - p1 == 4
    end
  end
end

# Prime.cosins.take(10)
# => [[3, 7], [7, 11], [13, 17], [19, 23], [37, 41], [43, 47], [67, 71], [79, 83], [97, 101], [103, 107]]
# Prime.cosins(100).to_a
# => [[3, 7], [7, 11], [13, 17], [19, 23], [37, 41], [43, 47], [67, 71], [79, 83]]