code: private boolean checkDkTaxNumber(final String ptaxNumber) {
      final int checkSum = ptaxNumber.charAt(9) - '0';
      final int sum = ((ptaxNumber.charAt(0) - '0') * 4 //
          + (ptaxNumber.charAt(1) - '0') * 2 //
          + (ptaxNumber.charAt(2) - '0') * 3 //
          + (ptaxNumber.charAt(3) - '0') * 7 //
          + (ptaxNumber.charAt(4) - '0') * 6 //
          + (ptaxNumber.charAt(5) - '0') * 5 //
          + (ptaxNumber.charAt(6) - '0') * 4 //
          + (ptaxNumber.charAt(7) - '0') * 3 //
          + (ptaxNumber.charAt(8) - '0') * 2) //
          % MODULO_11;
      int calculatedCheckSum = MODULO_11 - sum;
      if (calculatedCheckSum == 10) {
        calculatedCheckSum = 0;
      }
      return checkSum == calculatedCheckSum;
    }
docs: check the Tax Identification Number number, country version for Denmark.
  
  @param ptaxNumber vat id to check
  @return true if checksum is ok