Il numero romano CCXCI nel sistema decimale vale: 291.
CCXCI in latino si scrive ducenti nonaginta unus,
mentre in italiano duecentonovantuno.
CCLXXII, CCLXXIII, CCLXXIV, CCLXXV, CCLXXVI, CCLXXVII, CCLXXVIII, CCLXXIX, CCLXXX, CCLXXXI, CCLXXXII, CCLXXXIII, CCLXXXIV, CCLXXXV, CCLXXXVI, CCLXXXVII, CCLXXXVIII, CCLXXXIX, CCXC, CCXCII, CCXCIII, CCXCIV, CCXCV, CCXCVI, CCXCVII, CCXCVIII, CCXCIX, CCC, CCCI, CCCII, CCCIII, CCCIV, CCCV, CCCVI, CCCVII, CCCVIII, CCCIX, CCCX