65535 is the integer after 65534 and before 65536.

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

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 ${\displaystyle n}$ whose Euler totient has an aliquot sum that is ${\displaystyle n}$: ${\displaystyle \sigma (\varphi (65535))=65535}$, 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).