# File lib/active_merchant/billing/check.rb, line 52
      def valid_routing_number?
        d = routing_number.to_s.split('').map(&:to_i).select { |d| (0..9).include?(d) }
        case d.size
          when 9 then
            checksum = ((3 * (d[0] + d[3] + d[6])) +
                        (7 * (d[1] + d[4] + d[7])) +
                             (d[2] + d[5] + d[8])) % 10
            case checksum
              when 0 then true
              else        false
            end
          else false
        end
      end