21457728 has 42 divisors (see below), whose sum is σ = 61506354. Its totient is φ = 7152384.

The previous prime is 21457727. The next prime is 21457747. The reversal of 21457728 is 82775412.

It can be written as a sum of positive squares in only one way, i.e., 21455424 + 2304 = 4632^2 + 48^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21457692 and 21457701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21457721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 18051 + ... + 19202.

It is an arithmetic number, because the mean of its divisors is an integer number (1464437).

Almost surely, 2^21457728 is an apocalyptic number.

It is an amenable number.

21457728 is an abundant number, since it is smaller than the sum of its proper divisors (40048626).

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

21457728 is a wasteful number, since it uses less digits than its factorization.

21457728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37271 (or 37258 counting only the distinct ones).

The product of its digits is 31360, while the sum is 36.

The square root of 21457728 is about 4632.2486979868. The cubic root of 21457728 is about 277.8825306368.

The spelling of 21457728 in words is "twenty-one million, four hundred fifty-seven thousand, seven hundred twenty-eight".