21000824 has 32 divisors (see below), whose sum is σ = 42804720. Its totient is φ = 9601536.

The previous prime is 21000823. The next prime is 21000827. The reversal of 21000824 is 42800012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000821) 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, 10859 + ... + 12645.

Almost surely, 2^21000824 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 21000824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21402360).

21000824 is an abundant number, since it is smaller than the sum of its proper divisors (21803896).

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

21000824 is a wasteful number, since it uses less digits than its factorization.

21000824 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1919 (or 1915 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 17.

The square root of 21000824 is about 4582.6655998447. The cubic root of 21000824 is about 275.8960260886.

Adding to 21000824 its reverse (42800012), we get a palindrome (63800836).

The spelling of 21000824 in words is "twenty-one million, eight hundred twenty-four", and thus it is an aban number.