21397824 has 224 divisors, whose sum is σ = 75590400. Its totient is φ = 5806080.

The previous prime is 21397823. The next prime is 21397829. The reversal of 21397824 is 42879312.

It is a tau number, because it is divible by the number of its divisors (224).

It is a Harshad number since it is a multiple of its sum of digits (36).

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21397823) 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 31 ways as a sum of consecutive naturals, for example, 350754 + ... + 350814.

Almost surely, 2^21397824 is an apocalyptic number.

21397824 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21397824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37795200).

21397824 is an abundant number, since it is smaller than the sum of its proper divisors (54192576).

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

21397824 is a wasteful number, since it uses less digits than its factorization.

21397824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 118 (or 102 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 21397824 is about 4625.7782047997. The cubic root of 21397824 is about 277.6236994165.

The spelling of 21397824 in words is "twenty-one million, three hundred ninety-seven thousand, eight hundred twenty-four".