• 12 can be written using four 4's:
• 122 = 144 is the smallest square that contains exactly two digits '4'.
• There are 12 distinct pentominoes:
It is a Jordan-Polya number, since it can be written as 3! ⋅ 2!.
12 is nontrivially palindromic in base 5 and base 11.
12 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
12 is an esthetic number in base 10 and base 12, because in such bases its adjacent digits differ by 1.
It is a tau number, because it is divible by the number of its divisors (6).
12 is an admirable number.
It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.
12 is an idoneal number.
It is an alternating number because its digits alternate between odd and even.
It is a O'Halloran number.
It is the 9-th Perrin number.
12 is a nontrivial repdigit in base 5 and base 11.
It is a plaindrome in base 5, base 7, base 8, base 9, base 10 and base 11.
It is a nialpdrome in base 2, base 3, base 4, base 5, base 6, base 11 and base 12.
It is a zygodrome in base 2, base 5 and base 11.
It is a panconsummate number.
A polygon with 12 sides can be constructed with ruler and compass.
12 is a highly composite number, because it has more divisors than any smaller number.
12 is a superabundant number, because it has a larger abundancy index than any smaller number.
12 is the 3-rd pentagonal number.
It is an amenable number.
12 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
12 is a wasteful number, since it uses less digits than its factorization.
12 is an evil number, because the sum of its binary digits is even.
The square root of 12 is about 3.4641016151. The cubic root of 12 is about 2.2894284851.
Adding to 12 its reverse (21), we get a palindrome (33).
Multiplying 12 by its reverse (21), we get a palindrome (252).