21320 has 32 divisors (see below), whose sum is σ = 52920. Its totient is φ = 7680.

The previous prime is 21319. The next prime is 21323. The reversal of 21320 is 2312.

It can be written as a sum of positive squares in 4 ways, for example, as 7396 + 13924 = 86^2 + 118^2 .

It is a Harshad number since it is a multiple of its sum of digits (8).

It is a plaindrome in base 14.

It is a nialpdrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21298 and 21307.

It is not an unprimeable number, because it can be changed into a prime (21323) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 500 + ... + 540.

2²¹³²⁰ is an apocalyptic number.

21320 is a gapful number since it is divisible by the number (20) 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 21320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26460).

21320 is an abundant number, since it is smaller than the sum of its proper divisors (31600).

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

21320 is a wasteful number, since it uses less digits than its factorization.

21320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65 (or 61 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 8.

The square root of 21320 is about 146.0136979876. The cubic root of 21320 is about 27.7286717592.

Adding to 21320 its reverse (2312), we get a palindrome (23632).

The spelling of 21320 in words is "twenty-one thousand, three hundred twenty", and thus it is an iban number.