• 12 can be written using four 4's:

• 12^{2} = 144 is the smallest square that contains exactly two digits '4'.

• There are 12 distinct pentominoes:

12 has 6 divisors (see below), whose sum is σ = 28. Its totient is φ = 4.

The previous prime is 11. The next prime is 13. The reversal of 12 is 21.

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 an interprime number because it is at equal distance from previous prime (11) and next prime (13).

It is a tau number, because it is divible by the number of its divisors (6).

12 is an admirable number.

It is a Harshad number since it is a multiple of its sum of digits (3).

It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.

It is a nude number because it is divisible by every one of its digits and also a Zuckerman number because it is divisible by the product of its digits.

12 is an idoneal number.

It is an alternating number because its digits alternate between odd and even.

It is one of the 548 Lynch-Bell numbers.

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.

It is a pernicious number, because its binary representation contains a prime number (2) of ones.

A polygon with 12 sides can be constructed with ruler and compass.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3 + 4 + 5.

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.

It is a pronic number, being equal to 3×4.

12 is the 3-rd pentagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 12, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (14).

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 sum of its prime factors is 7 (or 5 counting only the distinct ones).

The product of its digits is 2, while the sum is 3.

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).

The spelling of 12 in words is "twelve", and thus it is an aban number, an iban number, an oban number, and an uban number.

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