21555328 has 32 divisors (see below), whose sum is σ = 43868160. Its totient is φ = 10545408.

The previous prime is 21555311. The next prime is 21555353. The reversal of 21555328 is 82355512.

It is a tau number, because it is divible by the number of its divisors (32).

It is a self number, because there is not a number n which added to its sum of digits gives 21555328.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4225 + ... + 7807.

It is an arithmetic number, because the mean of its divisors is an integer number (1370880).

Almost surely, 2^21555328 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 21555328, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21934080).

21555328 is an abundant number, since it is smaller than the sum of its proper divisors (22312832).

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

21555328 is an equidigital number, since it uses as much as digits as its factorization.

21555328 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3644 (or 3632 counting only the distinct ones).

The product of its digits is 12000, while the sum is 31.

The square root of 21555328 is about 4642.7715860249. The cubic root of 21555328 is about 278.3032076430.

The spelling of 21555328 in words is "twenty-one million, five hundred fifty-five thousand, three hundred twenty-eight".