enkele speciale gevallen:
49 = 40+9 = XL + IX = XLIX FOUT: IL
99 = 90+9 = XC + IX = XCIX FOUT: IC
490 = 400+90= CD + XC= CDXC FOUT: XD
499 = 400+90+9 = CD + XC + IX = CDXCIX FOUT: ID
990 = 900+90= CM + XC= CMXC FOUT: XM
999 = 900+90+9 = CM + XC + IX = CMXCIX FOUT: IM