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 2k-20321 is a prime.
It is a Duffinian number.
It is a nialpdrome in base 13.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20321.
220321 is an apocalyptic number.
It is an amenable number.
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 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.