Il numero romano MMCDXCI nel sistema decimale vale: 2491.
MMCDXCI in latino si scrive duo milia quadringenti nonaginta unus,
mentre in italiano duemilaquattrocentonovantuno.
MMCDLXXII, MMCDLXXIII, MMCDLXXIV, MMCDLXXV, MMCDLXXVI, MMCDLXXVII, MMCDLXXVIII, MMCDLXXIX, MMCDLXXX, MMCDLXXXI, MMCDLXXXII, MMCDLXXXIII, MMCDLXXXIV, MMCDLXXXV, MMCDLXXXVI, MMCDLXXXVII, MMCDLXXXVIII, MMCDLXXXIX, MMCDXC, MMCDXCII, MMCDXCIII, MMCDXCIV, MMCDXCV, MMCDXCVI, MMCDXCVII, MMCDXCVIII, MMCDXCIX, MMD, MMDI, MMDII, MMDIII, MMDIV, MMDV, MMDVI, MMDVII, MMDVIII, MMDIX, MMDX