21215728 has 20 divisors (see below), whose sum is σ = 43524000. Its totient is φ = 9983744.

The previous prime is 21215693. The next prime is 21215759. The reversal of 21215728 is 82751212.

It is a super-2 number, since 2×21215728² = 900214229139968, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21215696 and 21215705.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 38728 + ... + 39271.

It is an arithmetic number, because the mean of its divisors is an integer number (2176200).

Almost surely, 2^21215728 is an apocalyptic number.

It is an amenable number.

21215728 is an abundant number, since it is smaller than the sum of its proper divisors (22308272).

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

21215728 is a wasteful number, since it uses less digits than its factorization.

21215728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78024 (or 78018 counting only the distinct ones).

The product of its digits is 2240, while the sum is 28.

The square root of 21215728 is about 4606.0534082878. The cubic root of 21215728 is about 276.8339267001.

The spelling of 21215728 in words is "twenty-one million, two hundred fifteen thousand, seven hundred twenty-eight".