All 7-digit prime palindromes in the first 100.000 digits of PI

email.rb

class Email

  def self.arccot(x, unity)
     xpow = unity / x
     n = 1
     sign = 1
     sum = 0
     loop do
         term = xpow / n
         break if term == 0
         sum += sign * (xpow/n)
         xpow /= x*x
         n += 2
         sign = -sign
     end
     sum
  end

  def self.calc_pi(digits = 10000)
     fudge = 10
     unity = 10**(digits+fudge)
     pi = 4*(4*arccot(5, unity) - arccot(239, unity))
     pi / (10**fudge)
  end

  def self.prime?(n)
    return false if n%2 == 0
    i = 3
    while ( i <= Math.sqrt(n)) do
      return false if (n%i) == 0
      i += 2
    end
    true
  end

  def self.palindrome?(str)
    str == str.reverse
  end

  def self.find_email(digits)
    pi = calc_pi(digits).to_s
    (digits-7).times do |i|
      str = pi[0+i, 7]
      puts "position=#{i} | str=#{str}" if self.palindrome?(str) and self.prime?(str.to_i)
    end
  end

end

Why did you named you class "Email" ????