21056728 has 32 divisors (see below), whose sum is σ = 49224960. Its totient is φ = 8203680.

The previous prime is 21056723. The next prime is 21056743. The reversal of 21056728 is 82765012.

It is a self number, because there is not a number n which added to its sum of digits gives 21056728.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056723) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16476 + ... + 17707.

It is an arithmetic number, because the mean of its divisors is an integer number (1538280).

Almost surely, 2^21056728 is an apocalyptic number.

21056728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21056728 is an abundant number, since it is smaller than the sum of its proper divisors (28168232).

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

21056728 is a wasteful number, since it uses less digits than its factorization.

21056728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34207 (or 34203 counting only the distinct ones).

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 21056728 is about 4588.7610528333. The cubic root of 21056728 is about 276.1406200743.

The spelling of 21056728 in words is "twenty-one million, fifty-six thousand, seven hundred twenty-eight".