21838 has 8 divisors (see below), whose sum is σ = 33480. Its totient is φ = 10680.

The previous prime is 21821. The next prime is 21839. The reversal of 21838 is 83812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21839) 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, 33 + ... + 211.

It is an arithmetic number, because the mean of its divisors is an integer number (4185).

2²¹⁸³⁸ is an apocalyptic number.

21838 is a deficient number, since it is larger than the sum of its proper divisors (11642).

21838 is a wasteful number, since it uses less digits than its factorization.

21838 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 242.

The product of its digits is 384, while the sum is 22.

The square root of 21838 is about 147.7768588108. The cubic root of 21838 is about 27.9514464664.

Adding to 21838 its product of digits (384), we get a palindrome (22222).

It can be divided in two parts, 218 and 38, that added together give a 8-th power (256 = 2⁸).

The spelling of 21838 in words is "twenty-one thousand, eight hundred thirty-eight".