21045440 has 56 divisors (see below), whose sum is σ = 53980080. Its totient is φ = 7769088.

The previous prime is 21045433. The next prime is 21045457. The reversal of 21045440 is 4454012.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1631 + ... + 6689.

It is an arithmetic number, because the mean of its divisors is an integer number (963930).

Almost surely, 2^21045440 is an apocalyptic number.

21045440 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 21045440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26990040).

21045440 is an abundant number, since it is smaller than the sum of its proper divisors (32934640).

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

21045440 is a wasteful number, since it uses less digits than its factorization.

21045440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5089 (or 5079 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 20.

The square root of 21045440 is about 4587.5309263263. The cubic root of 21045440 is about 276.0912671631.

Adding to 21045440 its reverse (4454012), we get a palindrome (25499452).

The spelling of 21045440 in words is "twenty-one million, forty-five thousand, four hundred forty".