4. 16 (number) - Wikipedia
Link: https://en.wikipedia.org/wiki/16_(number)
Description: WEB16 is the ninth composite number, and a square number: 4 2 = 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 1, 2, 4 and 8 . Sixteen is the only integer that equals mn and nm, for some unequal integers m and n ( , , or vice versa). [1]