21712 has 20 divisors (see below), whose sum is σ = 44640. Its totient is φ = 10208.

The previous prime is 21701. The next prime is 21713.

21712 = 19² + 20² + ... + 41².

21712 is nontrivially palindromic in base 10.

It is a plaindrome in base 15.

It is a zygodrome in base 15.

It is a junction number, because it is equal to n+sod(n) for n = 21692 and 21701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21713) by changing a digit.

21712 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 339 + ... + 397.

It is an arithmetic number, because the mean of its divisors is an integer number (2232).

2²¹⁷¹² is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21712, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22320).

21712 is an abundant number, since it is smaller than the sum of its proper divisors (22928).

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

21712 is a wasteful number, since it uses less digits than its factorization.

21712 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90 (or 84 counting only the distinct ones).

The product of its digits is 28, while the sum is 13.

The square root of 21712 is about 147.3499236512. The cubic root of 21712 is about 27.8975850395.

The spelling of 21712 in words is "twenty-one thousand, seven hundred twelve", and thus it is an iban number.