16 is the ninth
composite number, and a
square number:
42 = 4 × 4 (the first non-unitary fourth-power
prime of the form
p4). It is the smallest number with exactly five
divisors, its proper divisors being , , and . Sixteen is the only integer that
equals mn and nm, for some unequal integers m and n (m=4, n=2, or vice versa). It has this property because 2^{2}=2\times 2. It is also equal to 32 (see
tetration). The aliquot sum of 16 is
15, within an
aliquot sequence of four composite members (16,
15,
9,
4,
3,
1,
0) that belong to the prime
3-aliquot tree. • Sixteen is the largest known integer , for which 2^n+1 is prime. • It is the first
Erdős–Woods number. • There are 16 partially ordered sets with four unlabeled elements. 16 is the only number that can be both the perimeter and area of the same square, due to 4^{2} being equal to 4\times 4. The
sedenions form a 16-dimensional
hypercomplex number system.
Hexadecimal Sixteen is the base of the
hexadecimal number system, which is used extensively in
computer science. == Technology ==