21028815 has 40 divisors (see below), whose sum is σ = 38071440. Its totient is φ = 11104128.

The previous prime is 21028771. The next prime is 21028823. The reversal of 21028815 is 51882012.

It is not a de Polignac number, because 21028815 - 2¹⁰ = 21027791 is a prime.

It is a super-2 number, since 2×21028815² = 884422120608450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 55296 + ... + 55674.

It is an arithmetic number, because the mean of its divisors is an integer number (951786).

Almost surely, 2^21028815 is an apocalyptic number.

21028815 is a deficient number, since it is larger than the sum of its proper divisors (17042625).

21028815 is a wasteful number, since it uses less digits than its factorization.

21028815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 533 (or 524 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 21028815 is about 4585.7185914533. The cubic root of 21028815 is about 276.0185479028.

The spelling of 21028815 in words is "twenty-one million, twenty-eight thousand, eight hundred fifteen".