LXXXI

LXXXI is the Roman numeral for the integer 81. It is formed from the symbols L (50), XXX (30), and I (1), added together to yield 81.

In Roman numeral notation, subtractive forms exist for certain values (for example XL for 40 or XC for 90). LXXXI does not use subtractive notation; it is an additive representation: 50 plus 30 plus 1. The arrangement also adheres to common rules limiting consecutive identical symbols, with XXX comprising three consecutive Xs.

Historically, LXXXI can be used to denote the year 81 AD or 81 BCE in dating, and the form appears in contexts such as chapter or volume numbering, clock faces, and other enumerations that employ Roman numerals. In modern usage, it is primarily encountered for stylistic or traditional reasons rather than for everyday arithmetic.

Mathematically, 81 is notable as a perfect square (9 squared) and as a power (3 to the fourth). Its prime factorization is 3^4. In other base systems, its representations differ, but in Roman numerals, the value is written as LXXXI as the additive combination of fifty, thirty, and one.

The form LXXXI is one of several ways to express the number 80 or 90 in the broader category of numerals that use L, X, and I. The immediate neighbors are LXXX (80) and LXXXII (82).