21055428 has 18 divisors (see below), whose sum is σ = 53223534. Its totient is φ = 7018464.

The previous prime is 21055409. The next prime is 21055429. The reversal of 21055428 is 82455012.

It is a happy number.

21055428 is nontrivially palindromic in base 13.

It can be written as a sum of positive squares in only one way, i.e., 20958084 + 97344 = 4578^2 + 312^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is not an unprimeable number, because it can be changed into a prime (21055429) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 292401 + ... + 292472.

It is an arithmetic number, because the mean of its divisors is an integer number (2956863).

Almost surely, 2^21055428 is an apocalyptic number.

It is an amenable number.

21055428 is an abundant number, since it is smaller than the sum of its proper divisors (32168106).

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

21055428 is a wasteful number, since it uses less digits than its factorization.

21055428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 584883 (or 584878 counting only the distinct ones).

The product of its (nonzero) digits is 3200, while the sum is 27.

The square root of 21055428 is about 4588.6194002118. The cubic root of 21055428 is about 276.1349371687.

The spelling of 21055428 in words is "twenty-one million, fifty-five thousand, four hundred twenty-eight".