The square root of 16 is 4.
It is a Jordan-Polya number, since it can be written as (2!)4.
16 is nontrivially palindromic in base 3, base 7 and base 15.
16 is an esthetic number in base 3, base 14 and base 16, because in such bases it adjacent digits differ by 1.
16 is an idoneal number.
It is a magnanimous number.
It is an Ulam number.
It is an alternating number because its digits alternate between odd and even.
It is a Duffinian number.
16 is an undulating number in base 3.
16 is a nontrivial repdigit in base 7 and base 15.
It is a plaindrome in base 6, base 7, base 9, base 10, base 11, base 12, base 13, base 14 and base 15.
It is a nialpdrome in base 2, base 4, base 5, base 7, base 8, base 15 and base 16.
It is a zygodrome in base 7 and base 15.
A polygon with 16 sides can be constructed with ruler and compass.
It is an impolite number, since it cannot be written as a nontrivial sum of consecutive naturals.
16 is the 4-th square number.
16 is the 3-rd centered pentagonal number.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 16
16 is an equidigital number, since it uses as much as digits as its factorization.
16 is an odious number, because the sum of its binary digits is odd.
The cubic root of 16 is about 2.5198420998.