21251728 has 40 divisors (see below), whose sum is σ = 44193600. Its totient is φ = 9869184.

The previous prime is 21251719. The next prime is 21251731. The reversal of 21251728 is 82715212.

It is a junction number, because it is equal to n+sod(n) for n = 21251696 and 21251705.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15453 + ... + 16771.

It is an arithmetic number, because the mean of its divisors is an integer number (1104840).

Almost surely, 2^21251728 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 21251728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22096800).

21251728 is an abundant number, since it is smaller than the sum of its proper divisors (22941872).

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

21251728 is a wasteful number, since it uses less digits than its factorization.

21251728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1399 (or 1393 counting only the distinct ones).

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

The square root of 21251728 is about 4609.9596527519. The cubic root of 21251728 is about 276.9904205005.

The spelling of 21251728 in words is "twenty-one million, two hundred fifty-one thousand, seven hundred twenty-eight".