21056640 has 128 divisors (see below), whose sum is σ = 73293120. Its totient is φ = 5099520.

The previous prime is 21056597. The next prime is 21056653. The reversal of 21056640 is 4665012.

It is a tau number, because it is divible by the number of its divisors (128).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21056640.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 20622 + ... + 21618.

Almost surely, 2^21056640 is an apocalyptic number.

21056640 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 21056640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36646560).

21056640 is an abundant number, since it is smaller than the sum of its proper divisors (52236480).

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

21056640 is a wasteful number, since it uses less digits than its factorization.

21056640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1030 (or 1018 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21056640 is about 4588.7514641785. The cubic root of 21056640 is about 276.1402353927.

The spelling of 21056640 in words is "twenty-one million, fifty-six thousand, six hundred forty".