999 (nine hundred ninety-nine or nine-nine-nine) is a natural number following 998 and preceding 1000.

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• ${\displaystyle 999=3^{3}\times 37}$, a Kaprekar number.^[1]
• a repdigit in decimal and hexatridecimal.
• a palindromic number in bases 10, 14 (515₁₄), and 36 (RR₃₆).
• the largest 3-digit decimal integer.
• the largest number in English not containing the letter 'o' in its name, when using short scale.
• A base-10 Harshad number because ${\displaystyle {\frac {999}{(9+9+9)}}=37}$, a whole number

• In some parts of the world, such as the UK and Commonwealth countries, 999 (pronounced as 9-9-9) is the emergency telephone number.
• 999 was a London punk band active during the 1970s.
• 999 is also the short name for the visual novel Nine Hours, Nine Persons, Nine Doors.
• 999 is the last 3 digit number.