21912 has 32 divisors (see below), whose sum is σ = 60480. Its totient is φ = 6560.

The previous prime is 21911. The next prime is 21929.

It is a happy number.

21912 is nontrivially palindromic in base 10.

It is a junction number, because it is equal to n+sod(n) for n = 21891 and 21900.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21911) 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 7 ways as a sum of consecutive naturals, for example, 223 + ... + 305.

It is an arithmetic number, because the mean of its divisors is an integer number (1890).

2²¹⁹¹² is an apocalyptic number.

21912 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21912, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30240).

21912 is an abundant number, since it is smaller than the sum of its proper divisors (38568).

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

21912 is a wasteful number, since it uses less digits than its factorization.

21912 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103 (or 99 counting only the distinct ones).

The product of its digits is 36, while the sum is 15.

The square root of 21912 is about 148.0270245597. The cubic root of 21912 is about 27.9829828571.

It can be divided in two parts, 219 and 12, that multiplied together give a triangular number (2628 = T₇₂).

The spelling of 21912 in words is "twenty-one thousand, nine hundred twelve".