Il numero romano MCCCXCI nel sistema decimale vale: 1391.
MCCCXCI in latino si scrive mille trecenti nonaginta unus,
mentre in italiano milletrecentonovantuno.
MCCCLXXII, MCCCLXXIII, MCCCLXXIV, MCCCLXXV, MCCCLXXVI, MCCCLXXVII, MCCCLXXVIII, MCCCLXXIX, MCCCLXXX, MCCCLXXXI, MCCCLXXXII, MCCCLXXXIII, MCCCLXXXIV, MCCCLXXXV, MCCCLXXXVI, MCCCLXXXVII, MCCCLXXXVIII, MCCCLXXXIX, MCCCXC, MCCCXCII, MCCCXCIII, MCCCXCIV, MCCCXCV, MCCCXCVI, MCCCXCVII, MCCCXCVIII, MCCCXCIX, MCD, MCDI, MCDII, MCDIII, MCDIV, MCDV, MCDVI, MCDVII, MCDVIII, MCDIX, MCDX