21612 has 12 divisors (see below), whose sum is σ = 50456. Its totient is φ = 7200.

The previous prime is 21611. The next prime is 21613.

21612 is nontrivially palindromic in base 10.

It is an interprime number because it is at equal distance from previous prime (21611) and next prime (21613).

It is a tau number, because it is divible by the number of its divisors (12).

It is a Harshad number since it is a multiple of its sum of digits (12), and also a Moran number because the ratio is a prime number: 1801 = 21612 / (2 + 1 + 6 + 1 + 2).

It is a nude number because it is divisible by every one of its digits.

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

It is not an unprimeable number, because it can be changed into a prime (21611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 889 + ... + 912.

2²¹⁶¹² is an apocalyptic number.

It is an amenable number.

21612 is an abundant number, since it is smaller than the sum of its proper divisors (28844).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25228).

21612 is a wasteful number, since it uses less digits than its factorization.

21612 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1808 (or 1806 counting only the distinct ones).

The product of its digits is 24, while the sum is 12.

The square root of 21612 is about 147.0102037275. The cubic root of 21612 is about 27.8546893678.

The spelling of 21612 in words is "twenty-one thousand, six hundred twelve".