def nth(index)
			if (!index.kind_of?(Integer))
				raise ArgumentError, "Expected an Integer for 'index' but got a #{index.class}."
			elsif (index >= self.len)
				return nil
			end
			return IPv4.new(self.network.addr + index)
		end
def nth(index)
			if (!index.kind_of?(Integer))
				raise ArgumentError, "Expected an Integer for 'index' but got a #{index.class}."
			elsif (index >= self.len)
				return nil
			end
			return IPv4.new(self.network.addr + index)
		end
nth returns the IPv4 at the given index.
 The size of the network may be determined with the len() method.
 If the range is exceeded then return nil.