20 lines
435 B
Ruby
20 lines
435 B
Ruby
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require 'openssl'
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factorial_primes = Enumerator.new do |y|
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fact = 1
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(1..).each do |i|
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fact *= i
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y << [i, "- 1", fact - 1] if OpenSSL::BN.new(fact - 1).prime?
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y << [i, "+ 1", fact + 1] if OpenSSL::BN.new(fact + 1).prime?
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end
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end
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factorial_primes.first(30).each do |a|
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s = a.last.to_s
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if s.size > 40 then
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puts "%d! %s = " % a.first(2) + "#{s[0,20]}...#{s[-20,20]}"
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else
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puts "%d! %s = %d" % a
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end
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end
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