21729824 has 24 divisors (see below), whose sum is σ = 42886620. Its totient is φ = 10838016.

The previous prime is 21729821. The next prime is 21729889. The reversal of 21729824 is 42892712.

It can be written as a sum of positive squares in 2 ways, for example, as 20976400 + 753424 = 4580^2 + 868^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21729821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21032 + ... + 22040.

Almost surely, 2^21729824 is an apocalyptic number.

It is an amenable number.

21729824 is a deficient number, since it is larger than the sum of its proper divisors (21156796).

21729824 is a wasteful number, since it uses less digits than its factorization.

21729824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1692 (or 1684 counting only the distinct ones).

The product of its digits is 16128, while the sum is 35.

The square root of 21729824 is about 4661.5259304224. The cubic root of 21729824 is about 279.0521692589.

The spelling of 21729824 in words is "twenty-one million, seven hundred twenty-nine thousand, eight hundred twenty-four".