21804840 has 96 divisors (see below), whose sum is σ = 72825480. Its totient is φ = 5654016.

The previous prime is 21804833. The next prime is 21804857. The reversal of 21804840 is 4840812.

21804840 is a `hidden beast` number, since 2 + 180 + 484 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 16016004 + 5788836 = 4002^2 + 2406^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 12502 + ... + 14138.

Almost surely, 2^21804840 is an apocalyptic number.

21804840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21804840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36412740).

21804840 is an abundant number, since it is smaller than the sum of its proper divisors (51020640).

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

21804840 is a wasteful number, since it uses less digits than its factorization.

21804840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1691 (or 1684 counting only the distinct ones).

The product of its (nonzero) digits is 2048, while the sum is 27.

The square root of 21804840 is about 4669.5652902599. The cubic root of 21804840 is about 279.3729163696.

The spelling of 21804840 in words is "twenty-one million, eight hundred four thousand, eight hundred forty".