21801728 has 36 divisors (see below), whose sum is σ = 46873008. Its totient is φ = 10060800.

The previous prime is 21801727. The next prime is 21801737. The reversal of 21801728 is 82710812.

It is a self number, because there is not a number n which added to its sum of digits gives 21801728.

It is not an unprimeable number, because it can be changed into a prime (21801727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 53 + ... + 6603.

It is an arithmetic number, because the mean of its divisors is an integer number (1302028).

Almost surely, 2^21801728 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 21801728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23436504).

21801728 is an abundant number, since it is smaller than the sum of its proper divisors (25071280).

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

21801728 is an equidigital number, since it uses as much as digits as its factorization.

21801728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6580 (or 6566 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 21801728 is about 4669.2320567734. The cubic root of 21801728 is about 279.3596249799.

The spelling of 21801728 in words is "twenty-one million, eight hundred one thousand, seven hundred twenty-eight".