21181728 has 48 divisors (see below), whose sum is σ = 58877280. Its totient is φ = 6644736.

The previous prime is 21181703. The next prime is 21181729. The reversal of 21181728 is 82718112.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (48).

It is a junction number, because it is equal to n+sod(n) for n = 21181695 and 21181704.

It is not an unprimeable number, because it can be changed into a prime (21181729) 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, 4858 + ... + 8121.

It is an arithmetic number, because the mean of its divisors is an integer number (1226610).

Almost surely, 2^21181728 is an apocalyptic number.

It is an amenable number.

21181728 is an abundant number, since it is smaller than the sum of its proper divisors (37695552).

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

21181728 is a wasteful number, since it uses less digits than its factorization.

21181728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13009 (or 13001 counting only the distinct ones).

The product of its digits is 1792, while the sum is 30.

The square root of 21181728 is about 4602.3611331576. The cubic root of 21181728 is about 276.6859643642.

The spelling of 21181728 in words is "twenty-one million, one hundred eighty-one thousand, seven hundred twenty-eight".