21438 has 16 divisors (see below), whose sum is σ = 47760. Its totient is φ = 7128.

The previous prime is 21433. The next prime is 21467. The reversal of 21438 is 83412.

It is a happy number.

21438 is an esthetic number in base 15, because in such base its adjacent digits differ by 1.

It is a Harshad number since it is a multiple of its sum of digits (18).

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

It is a nialpdrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 21438.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21433) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 145 + ... + 252.

It is an arithmetic number, because the mean of its divisors is an integer number (2985).

2²¹⁴³⁸ is an apocalyptic number.

21438 is an abundant number, since it is smaller than the sum of its proper divisors (26322).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23880).

21438 is a wasteful number, since it uses less digits than its factorization.

21438 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408 (or 402 counting only the distinct ones).

The product of its digits is 192, while the sum is 18.

The square root of 21438 is about 146.4172121029. The cubic root of 21438 is about 27.7797343807.

It can be divided in two parts, 214 and 38, that added together give a palindrome (252).

The spelling of 21438 in words is "twenty-one thousand, four hundred thirty-eight".