21085728 has 48 divisors (see below), whose sum is σ = 55742400. Its totient is φ = 6978816.

The previous prime is 21085721. The next prime is 21085739. The reversal of 21085728 is 82758012.

It is a tau number, because it is divible by the number of its divisors (48).

It is not an unprimeable number, because it can be changed into a prime (21085721) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14373 + ... + 15771.

It is an arithmetic number, because the mean of its divisors is an integer number (1161300).

Almost surely, 2^21085728 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21085728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27871200).

21085728 is an abundant number, since it is smaller than the sum of its proper divisors (34656672).

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

21085728 is a wasteful number, since it uses less digits than its factorization.

21085728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1569 (or 1561 counting only the distinct ones).

The product of its (nonzero) digits is 8960, while the sum is 33.

The square root of 21085728 is about 4591.9198599279. The cubic root of 21085728 is about 276.2673318228.

The spelling of 21085728 in words is "twenty-one million, eighty-five thousand, seven hundred twenty-eight".