21157824 has 56 divisors (see below), whose sum is σ = 56327040. Its totient is φ = 7009024.

The previous prime is 21157817. The next prime is 21157831. The reversal of 21157824 is 42875112.

It is an interprime number because it is at equal distance from previous prime (21157817) and next prime (21157831).

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 21157791 and 21157800.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 50287 + ... + 50705.

It is an arithmetic number, because the mean of its divisors is an integer number (1005840).

Almost surely, 2^21157824 is an apocalyptic number.

21157824 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 21157824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28163520).

21157824 is an abundant number, since it is smaller than the sum of its proper divisors (35169216).

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

21157824 is a wasteful number, since it uses less digits than its factorization.

21157824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 697 (or 687 counting only the distinct ones).

The product of its digits is 4480, while the sum is 30.

The square root of 21157824 is about 4599.7634721798. The cubic root of 21157824 is about 276.5818433213.

The spelling of 21157824 in words is "twenty-one million, one hundred fifty-seven thousand, eight hundred twenty-four".