21055728 has 20 divisors (see below), whose sum is σ = 54394088. Its totient is φ = 7018560.

The previous prime is 21055717. The next prime is 21055733. The reversal of 21055728 is 82755012.

It is a junction number, because it is equal to n+sod(n) for n = 21055695 and 21055704.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 219283 + ... + 219378.

Almost surely, 2^21055728 is an apocalyptic number.

It is an amenable number.

21055728 is an abundant number, since it is smaller than the sum of its proper divisors (33338360).

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

21055728 is a wasteful number, since it uses less digits than its factorization.

21055728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438672 (or 438666 counting only the distinct ones).

The product of its (nonzero) digits is 5600, while the sum is 30.

The square root of 21055728 is about 4588.6520896664. The cubic root of 21055728 is about 276.1362486292.

The spelling of 21055728 in words is "twenty-one million, fifty-five thousand, seven hundred twenty-eight".