21540724 has 12 divisors (see below), whose sum is σ = 37993984. Its totient is φ = 10685304.

The previous prime is 21540709. The next prime is 21540731. The reversal of 21540724 is 42704512.

It is a hoax number, since the sum of its digits (25) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20694 + ... + 21709.

Almost surely, 2^21540724 is an apocalyptic number.

It is an amenable number.

21540724 is a deficient number, since it is larger than the sum of its proper divisors (16453260).

21540724 is a wasteful number, since it uses less digits than its factorization.

21540724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42534 (or 42532 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 25.

The square root of 21540724 is about 4641.1985520984. The cubic root of 21540724 is about 278.2403421607.

The spelling of 21540724 in words is "twenty-one million, five hundred forty thousand, seven hundred twenty-four".