21804720 has 80 divisors (see below), whose sum is σ = 77256960. Its totient is φ = 4983552.

The previous prime is 21804719. The next prime is 21804737. The reversal of 21804720 is 2740812.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4810 + ... + 8169.

It is an arithmetic number, because the mean of its divisors is an integer number (965712).

Almost surely, 2^21804720 is an apocalyptic number.

21804720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21804720 is an abundant number, since it is smaller than the sum of its proper divisors (55452240).

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

21804720 is a wasteful number, since it uses less digits than its factorization.

21804720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13002 (or 12996 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 21804720 is about 4669.5524410804. The cubic root of 21804720 is about 279.3724038716.

The spelling of 21804720 in words is "twenty-one million, eight hundred four thousand, seven hundred twenty".