21424 has 20 divisors (see below), whose sum is σ = 45136. Its totient is φ = 9792.

The previous prime is 21419. The next prime is 21433. The reversal of 21424 is 42412.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

21424 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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, 157 + ... + 259.

2²¹⁴²⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21424, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22568).

21424 is an abundant number, since it is smaller than the sum of its proper divisors (23712).

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

21424 is a wasteful number, since it uses less digits than its factorization.

21424 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124 (or 118 counting only the distinct ones).

The product of its digits is 64, while the sum is 13.

The square root of 21424 is about 146.3693957083. The cubic root of 21424 is about 27.7736859158.

Adding to 21424 its reverse (42412), we get a palindrome (63836).

The spelling of 21424 in words is "twenty-one thousand, four hundred twenty-four", and thus it is an iban number.