21317728 has 48 divisors (see below), whose sum is σ = 44906400. Its totient is φ = 9926656.

The previous prime is 21317719. The next prime is 21317729. The reversal of 21317728 is 82771312.

It is a self number, because there is not a number n which added to its sum of digits gives 21317728.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21317729) 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, 80925 + ... + 81187.

It is an arithmetic number, because the mean of its divisors is an integer number (935550).

Almost surely, 2^21317728 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 21317728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22453200).

21317728 is an abundant number, since it is smaller than the sum of its proper divisors (23588672).

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

21317728 is a wasteful number, since it uses less digits than its factorization.

21317728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439 (or 431 counting only the distinct ones).

The product of its digits is 4704, while the sum is 31.

The square root of 21317728 is about 4617.1125175807. The cubic root of 21317728 is about 277.2768674078.

The spelling of 21317728 in words is "twenty-one million, three hundred seventeen thousand, seven hundred twenty-eight".