Il numero romano MDCXCI nel sistema decimale vale: 1691.
MDCXCI in latino si scrive mille sescenti nonaginta unus,
mentre in italiano milleseicentonovantuno.
MDCLXXII, MDCLXXIII, MDCLXXIV, MDCLXXV, MDCLXXVI, MDCLXXVII, MDCLXXVIII, MDCLXXIX, MDCLXXX, MDCLXXXI, MDCLXXXII, MDCLXXXIII, MDCLXXXIV, MDCLXXXV, MDCLXXXVI, MDCLXXXVII, MDCLXXXVIII, MDCLXXXIX, MDCXC, MDCXCII, MDCXCIII, MDCXCIV, MDCXCV, MDCXCVI, MDCXCVII, MDCXCVIII, MDCXCIX, MDCC, MDCCI, MDCCII, MDCCIII, MDCCIV, MDCCV, MDCCVI, MDCCVII, MDCCVIII, MDCCIX, MDCCX