65535 is the integer after 65534 and before 65536.

It is the maximum value of an unsigned 16-bit integer.

In mathematics

65535 is the sum of 20 through 215 (20 + 21 + 22 + ... + 215) and is therefore a repdigit in base 2 (1111111111111111), in base 4 (33333333), and in base 16 (FFFF).

It is the ninth number n {\displaystyle n} whose Euler totient has an aliquot sum that is n {\displaystyle n}: σ ( φ ( 65535 ) ) = 65535 {\displaystyle \sigma (\varphi (65535))=65535}, and the twenty-eighth perfect totient number equal to the sum of its iterated totients.

65535 is the fifteenth 626-gonal number, the fifth 6555-gonal number, and the third 21846-gonal number.

65535 is the product of the first four Fermat primes: 65535 = (2 + 1)(4 + 1)(16 + 1)(256 + 1). Because of this property, it is possible to construct with compass and straightedge a regular polygon with 65535 sides (see, constructible polygon).

In computing

  • 65535 occurs frequently in the field of computing because it is 2 16 − 1 {\displaystyle 2^{16}-1} (one less than 2 to the 16th power), which is the highest number that can be represented by an unsigned 16-bit binary number. Some computer programming environments may have predefined constant values representing 65535, with names like MAX_UNSIGNED_SHORT.
  • In older computers with processors having a 16-bit address bus such as the MOS Technology 6502 popular in the 1970s and the Zilog Z80, 65535 (FFFF16) is the highest addressable memory location, with 0 (000016) being the lowest. Such processors thus support at most 64 KiB of total byte-addressable memory.
  • In Internet protocols, 65535 is also the number of TCP and UDP ports available for use, since port 0 is reserved.
  • In some implementations of Tiny BASIC, entering a command that divides any number by zero will return 65535.
  • In Microsoft Word 2011 for Mac, 65535 is the highest line number that will be displayed.
  • In HTML, 65535 is the decimal value of the web color Aqua (#00FFFF) .
  • in Dragon Quest 1, this is the number of experience points needed to reach the maximum character level of 30.
  • In Fallout 4, level 65535 is the last possible level that the player can reach as there is no level cap. Gaining one more after this causes the game to crash.

See also