20321 has 4 divisors (see below), whose sum is σ = 23232. Its totient is φ = 17412.

The previous prime is 20297. The next prime is 20323. The reversal of 20321 is 12302.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12302 = 2 ⋅6151.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20321 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 20299 and 20308.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20321.

It is not an unprimeable number, because it can be changed into a prime (20323) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1445 + ... + 1458.

It is an arithmetic number, because the mean of its divisors is an integer number (5808).

2²⁰³²¹ is an apocalyptic number.

It is an amenable number.

20321 is a deficient number, since it is larger than the sum of its proper divisors (2911).

20321 is an equidigital number, since it uses as much as digits as its factorization.

20321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2910.

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

The square root of 20321 is about 142.5517449911. The cubic root of 20321 is about 27.2886274287.

Adding to 20321 its reverse (12302), we get a palindrome (32623).

The spelling of 20321 in words is "twenty thousand, three hundred twenty-one", and thus it is an iban number.