Il numero romano CDXX nel sistema decimale vale: 420.
CDXX in latino si scrive quadringenti viginti,
mentre in italiano quattrocentoventi.
CDI, CDII, CDIII, CDIV, CDV, CDVI, CDVII, CDVIII, CDIX, CDX, CDXI, CDXII, CDXIII, CDXIV, CDXV, CDXVI, CDXVII, CDXVIII, CDXIX, CDXXI, CDXXII, CDXXIII, CDXXIV, CDXXV, CDXXVI, CDXXVII, CDXXVIII, CDXXIX, CDXXX, CDXXXI, CDXXXII, CDXXXIII, CDXXXIV, CDXXXV, CDXXXVI, CDXXXVII, CDXXXVIII, CDXXXIX