LXVI

LXVI is the Roman numeral for the number 66. It is formed by the symbols L (50), X (10), V (5), and I (1) arranged as LXVI, which adds up to 50 + 10 + 5 + 1 = 66. This representation uses additive notation, and does not employ subtractive forms such as IV or XL in this order.

In usage, LXVI appears in contexts that require Roman numerals to indicate a count or a year. It can label the sixty-sixth item in a series, a chapter or edition in a book, or denote a year when paired with an era marker (for example, 66 CE or 66 BCE). Its appearance is common on inscriptions, monuments, clocks, and other settings where Roman numerals retain traditional or ceremonial function.

Beyond its basic value, the number 66 has mathematical properties that are sometimes noted in numeric contexts. It is a composite number with prime factorization 2 × 3 × 11. It is also the sum of consecutive integers 21 + 22 + 23 and is the 11th triangular number, equal to 66.

See also: Roman numerals, numbers, 66 (number).