Il numero romano MCDXCI nel sistema decimale vale: 1491.
MCDXCI in latino si scrive mille quadringenti nonaginta unus,
mentre in italiano millequattrocentonovantuno.
MCDLXXII, MCDLXXIII, MCDLXXIV, MCDLXXV, MCDLXXVI, MCDLXXVII, MCDLXXVIII, MCDLXXIX, MCDLXXX, MCDLXXXI, MCDLXXXII, MCDLXXXIII, MCDLXXXIV, MCDLXXXV, MCDLXXXVI, MCDLXXXVII, MCDLXXXVIII, MCDLXXXIX, MCDXC, MCDXCII, MCDXCIII, MCDXCIV, MCDXCV, MCDXCVI, MCDXCVII, MCDXCVIII, MCDXCIX, MD, MDI, MDII, MDIII, MDIV, MDV, MDVI, MDVII, MDVIII, MDIX, MDX