Il numero romano MMMCMXCI nel sistema decimale vale: 3991.
MMMCMXCI in latino si scrive tria milia nongenti nonaginta unus,
mentre in italiano tremilanovecentonovantuno.
MMMCMLXXII, MMMCMLXXIII, MMMCMLXXIV, MMMCMLXXV, MMMCMLXXVI, MMMCMLXXVII, MMMCMLXXVIII, MMMCMLXXIX, MMMCMLXXX, MMMCMLXXXI, MMMCMLXXXII, MMMCMLXXXIII, MMMCMLXXXIV, MMMCMLXXXV, MMMCMLXXXVI, MMMCMLXXXVII, MMMCMLXXXVIII, MMMCMLXXXIX, MMMCMXC, MMMCMXCII, MMMCMXCIII, MMMCMXCIV, MMMCMXCV, MMMCMXCVI, MMMCMXCVII, MMMCMXCVIII, MMMCMXCIX, MMMM, MMMMI, MMMMII, MMMMIII, MMMMIV, MMMMV, MMMMVI, MMMMVII, MMMMVIII, MMMMIX, MMMMX