18021 has 4 divisors (see below), whose sum is σ = 24032. Its totient is φ = 12012.

The previous prime is 18013. The next prime is 18041. The reversal of 18021 is 12081.

It is a happy number.

18021 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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: 12081 = 3 ⋅4027.

It is not a de Polignac number, because 18021 - 2³ = 18013 is a prime.

It is a D-number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 17988 and 18006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18041) 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 3 ways as a sum of consecutive naturals, for example, 3001 + ... + 3006.

It is an arithmetic number, because the mean of its divisors is an integer number (6008).

2¹⁸⁰²¹ is an apocalyptic number.

It is an amenable number.

18021 is a deficient number, since it is larger than the sum of its proper divisors (6011).

18021 is an equidigital number, since it uses as much as digits as its factorization.

18021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6010.

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 18021 is about 134.2423182160. The cubic root of 18021 is about 26.2176017533.

The spelling of 18021 in words is "eighteen thousand, twenty-one".