21857904 has 80 divisors (see below), whose sum is σ = 66067200. Its totient is φ = 6899904.

The previous prime is 21857897. The next prime is 21857933. The reversal of 21857904 is 40975812.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6877 + ... + 9539.

It is an arithmetic number, because the mean of its divisors is an integer number (825840).

Almost surely, 2^21857904 is an apocalyptic number.

21857904 is a gapful number since it is divisible by the number (24) 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 21857904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33033600).

21857904 is an abundant number, since it is smaller than the sum of its proper divisors (44209296).

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

21857904 is a wasteful number, since it uses less digits than its factorization.

21857904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2699 (or 2687 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The square root of 21857904 is about 4675.2437369617. The cubic root of 21857904 is about 279.5993589847.

The spelling of 21857904 in words is "twenty-one million, eight hundred fifty-seven thousand, nine hundred four".