65,536

65536 is the natural number following 65535 and preceding 65537.

65536 is a power of two: ${\displaystyle 2^{16}}$ (2 to the 16th power).

65536 is the smallest number with exactly 17 divisors (but there are smaller numbers with more than 17 divisors; e.g., 180 has 18 divisors) (sequence A005179 in the OEIS).

65536 is ${\displaystyle 2^{2^{2^{2}}}}$, so in tetration notation 65536 is ⁴2.

When expressed using Knuth's up-arrow notation, 65536 is ${\displaystyle 2\uparrow 16}$, which is equal to ${\displaystyle 2\uparrow 2\uparrow 2\uparrow 2}$, which is equivalent to ${\displaystyle 2\uparrow \uparrow 4}$ or ${\displaystyle 2\uparrow \uparrow \uparrow 3}$.

As ${\displaystyle ^{2}2}$ is also equal to 4, or ${\displaystyle 2\uparrow \uparrow 2=4}$,

${\displaystyle ^{4}2}$ can thus be written as ${\displaystyle ^{^{2}2}2}$, or ${\displaystyle 2\uparrow \uparrow (2\uparrow \uparrow 2)}$, or as the pentation ${\displaystyle 2[5]3}$ (hyperoperation notation).

65536 is a superperfect number – a number such that σ(σ(n)) = 2n.