21731328 has 120 divisors (see below), whose sum is σ = 65405340. Its totient is φ = 7188480.

The previous prime is 21731317. The next prime is 21731363. The reversal of 21731328 is 82313712.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 165823 + ... + 165953.

Almost surely, 2^21731328 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 21731328, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32702670).

21731328 is an abundant number, since it is smaller than the sum of its proper divisors (43674012).

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

21731328 is an equidigital number, since it uses as much as digits as its factorization.

21731328 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 165 (or 136 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21731328 is about 4661.6872481967. The cubic root of 21731328 is about 279.0586071816.

The spelling of 21731328 in words is "twenty-one million, seven hundred thirty-one thousand, three hundred twenty-eight".