21321728 has 48 divisors (see below), whose sum is σ = 44226000. Its totient is φ = 10264576.

The previous prime is 21321709. The next prime is 21321733. The reversal of 21321728 is 82712312.

It is a junction number, because it is equal to n+sod(n) for n = 21321697 and 21321706.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 59213 + ... + 59571.

It is an arithmetic number, because the mean of its divisors is an integer number (921375).

Almost surely, 2^21321728 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 21321728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22113000).

21321728 is an abundant number, since it is smaller than the sum of its proper divisors (22904272).

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

21321728 is an equidigital number, since it uses as much as digits as its factorization.

21321728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 410 (or 390 counting only the distinct ones).

The product of its digits is 1344, while the sum is 26.

The square root of 21321728 is about 4617.5456684260. The cubic root of 21321728 is about 277.2942088135.

The spelling of 21321728 in words is "twenty-one million, three hundred twenty-one thousand, seven hundred twenty-eight".