Roman Numerals +

(Latin numbers as cardinals, "quantities"; and as ordinals, "showing order" or "designating a place in an ordered sequence")

XVI; sedecim, sextus decimus
Cardinal: sixteen, Ordinal: sixteenth
XVII; septemdecim, septimus decimus
Cardinal: seventeen, Ordinal: seventeenth
XVIII; duodevinginti/octodecim, duodevicesimus/octavusdecimus
Cardinal: eighteen, Ordinal: eighteenth
XIX; undeviginti/novemdecim, undevicesimus/novemdecimus
Cardinal: nineteen, Ordinal: nineteenth
XX; viginti, vicesimus
Cardinal: twenty, Ordinal: twentieth
XXI; unus et viginti, unetvice(n)simus
Cardinal: twenty-one, Ordinal: twenty-first
XXII; duoetviginti, duoetvice(n)simus
Cardinal: twenty-two, Ordinal: twenty-second
XXVIII; duodetriginta, duodetriginta
Cardinal: twenty-eight, Ordinal: twenty-eighth
XXIX; undetriginta, undetrice(n)simus
Cardinal: twenty-nine, Ordinal: twenty-ninth
XXX; triginta, trice(n)simus
Cardinal: thirty, Ordinal: thirtieth