21857440 has 72 divisors (see below), whose sum is σ = 56809620. Its totient is φ = 7941120.

The previous prime is 21857431. The next prime is 21857447. The reversal of 21857440 is 4475812.

It can be written as a sum of positive squares in 2 ways, for example, as 19749136 + 2108304 = 4444^2 + 1452^2 .

It is not an unprimeable number, because it can be changed into a prime (21857447) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18796 + ... + 19924.

Almost surely, 2^21857440 is an apocalyptic number.

21857440 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 21857440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28404810).

21857440 is an abundant number, since it is smaller than the sum of its proper divisors (34952180).

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

21857440 is a wasteful number, since it uses less digits than its factorization.

21857440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1166 (or 1147 counting only the distinct ones).

The product of its (nonzero) digits is 8960, while the sum is 31.

The square root of 21857440 is about 4675.1941136171. The cubic root of 21857440 is about 279.5973805239.

The spelling of 21857440 in words is "twenty-one million, eight hundred fifty-seven thousand, four hundred forty".