21005724 has 24 divisors (see below), whose sum is σ = 50595328. Its totient is φ = 6775920.

The previous prime is 21005713. The next prime is 21005737. The reversal of 21005724 is 42750012.

It is a self number, because there is not a number n which added to its sum of digits gives 21005724.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27862 + ... + 28605.

Almost surely, 2^21005724 is an apocalyptic number.

It is an amenable number.

21005724 is an abundant number, since it is smaller than the sum of its proper divisors (29589604).

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

21005724 is a wasteful number, since it uses less digits than its factorization.

21005724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56505 (or 56503 counting only the distinct ones).

The product of its (nonzero) digits is 560, while the sum is 21.

The square root of 21005724 is about 4583.2001920056. The cubic root of 21005724 is about 275.9174821578.

Adding to 21005724 its reverse (42750012), we get a palindrome (63755736).

The spelling of 21005724 in words is "twenty-one million, five thousand, seven hundred twenty-four".