18421 has 6 divisors (see below), whose sum is σ = 20130. Its totient is φ = 16848.

The previous prime is 18413. The next prime is 18427. The reversal of 18421 is 12481.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 196 + 18225 = 14^2 + 135^2 .

It is not a de Polignac number, because 18421 - 2³ = 18413 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 = 18395 and 18404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18427) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 115 + ... + 223.

It is an arithmetic number, because the mean of its divisors is an integer number (3355).

2¹⁸⁴²¹ is an apocalyptic number.

It is an amenable number.

18421 is a deficient number, since it is larger than the sum of its proper divisors (1709).

18421 is a wasteful number, since it uses less digits than its factorization.

18421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 135 (or 122 counting only the distinct ones).

The product of its digits is 64, while the sum is 16.

The square root of 18421 is about 135.7239846158. The cubic root of 18421 is about 26.4101621423.

The spelling of 18421 in words is "eighteen thousand, four hundred twenty-one".