21839724 has 18 divisors (see below), whose sum is σ = 55206060. Its totient is φ = 7279896.

The previous prime is 21839723. The next prime is 21839737. The reversal of 21839724 is 42793812.

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 606659 = 21839724 / (2 + 1 + 8 + 3 + 9 + 7 + 2 + 4).

It is not an unprimeable number, because it can be changed into a prime (21839723) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 303294 + ... + 303365.

Almost surely, 2^21839724 is an apocalyptic number.

It is an amenable number.

21839724 is an abundant number, since it is smaller than the sum of its proper divisors (33366336).

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

21839724 is a wasteful number, since it uses less digits than its factorization.

21839724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 606669 (or 606664 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 21839724 is about 4673.2990488519. The cubic root of 21839724 is about 279.5218198899.

The spelling of 21839724 in words is "twenty-one million, eight hundred thirty-nine thousand, seven hundred twenty-four".