class Integer

def even?

Standard in ruby 1.8.7+. See official documentation[http://ruby-doc.org/core-1.9/classes/Fixnum.html] 
def even?
  self[0].zero?
end unless method_defined? :even?

def odd?

Standard in ruby 1.8.7+. See official documentation[http://ruby-doc.org/core-1.9/classes/Fixnum.html] 
def odd?
  !even?
end unless method_defined? :odd?

def ord

Standard in ruby 1.8.7+. See official documentation[http://ruby-doc.org/core-1.9/classes/Fixnum.html] 
def ord
  self
end unless method_defined? :ord

def pred

Standard in ruby 1.8.7+. See official documentation[http://ruby-doc.org/core-1.9/classes/Fixnum.html] 
def pred
  self - 1
end unless method_defined? :pred

def prime?

Returns true if +self+ is a prime number, false for a composite. 
def prime?
  Prime.prime?(self)
end

def prime_division(generator = Prime::Generator23.new)

See Prime#prime_division for more details.

Returns the factorization of +self+. 
def prime_division(generator = Prime::Generator23.new)
  Prime.prime_division(self, generator)
end

def round_with_digits(ndigits=0) 

def round_with_digits(ndigits=0)
  ndigits = Backports::coerce_to_int(ndigits)
  case
  when ndigits.zero?
    self
  when ndigits > 0
    Float(self)
  else
    pow = 10 ** (-ndigits)
    remain = self % pow
    comp = self < 0 ? :<= : :<
    remain -= pow unless remain.send(comp, pow / 2)
    self - remain
  end
end