 Especially on tombstones and other funerary inscriptions 5 and 50 have been occasionally written and instead of and , and there are instances such as and rather than or .The irregular use of subtractive notation, such as for 17, for 18, for 97, for 98, and for 99 have been occasionally used.A possible explanation is that the word for 18 in Latin is "duodeviginti", literally "two from twenty".