3999

3999 is a natural number that follows 3998 and precedes 4000. In decimal notation it is written as 3999. The number is odd and composite, with prime factorization 3 × 31 × 43. Its digit sum is 30, so it is divisible by 3 but not by 9.

In common numeral systems, 3999 has several representations: binary 111110011111, octal 7637, and hexadecimal 0xF9F. In Roman numerals it is MMMCMXCIX, adding up three thousands, a nine hundred, ninety, and nine.

Cultural and mathematical context: 3999 is often noted as a near-4000 value and is sometimes used in fiction and examples as a far-future reference point, given that 4000 is a round milestone. It serves as a convenient example of a four-digit composite number with a compact factorization, and its representations across bases illustrate typical conversions between systems.

In computing and number theory, 3999 fits within standard fixed-width word sizes (for example it is less than 2^12, or 4096) and can be efficiently represented in binary, hexadecimal, or octal without special encoding. Its proximity to 4000 and its multiple small prime factors make it a straightforward test case for basic arithmetic and base-conversion demonstrations.