21028520 has 16 divisors (see below), whose sum is σ = 47314260. Its totient is φ = 8411392.

The previous prime is 21028517. The next prime is 21028549. The reversal of 21028520 is 2582012.

It can be written as a sum of positive squares in 2 ways, for example, as 20666116 + 362404 = 4546^2 + 602^2 .

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

It is a junction number, because it is equal to n+sod(n) for n = 21028492 and 21028501.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 262817 + ... + 262896.

Almost surely, 2^21028520 is an apocalyptic number.

21028520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21028520 is an abundant number, since it is smaller than the sum of its proper divisors (26285740).

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

21028520 is a wasteful number, since it uses less digits than its factorization.

21028520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 525724 (or 525720 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 20.

The square root of 21028520 is about 4585.6864262616. The cubic root of 21028520 is about 276.0172572000.

The spelling of 21028520 in words is "twenty-one million, twenty-eight thousand, five hundred twenty".