21308728 has 48 divisors (see below), whose sum is σ = 48940200. Its totient is φ = 8648640.

The previous prime is 21308723. The next prime is 21308731. The reversal of 21308728 is 82780312.

It is a self number, because there is not a number n which added to its sum of digits gives 21308728.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21308723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6018 + ... + 8878.

Almost surely, 2^21308728 is an apocalyptic number.

21308728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21308728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24470100).

21308728 is an abundant number, since it is smaller than the sum of its proper divisors (27631472).

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

21308728 is a wasteful number, since it uses less digits than its factorization.

21308728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2900 (or 2889 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 31.

The square root of 21308728 is about 4616.1377795729. The cubic root of 21308728 is about 277.2378413122.

The spelling of 21308728 in words is "twenty-one million, three hundred eight thousand, seven hundred twenty-eight".