21097728 has 54 divisors (see below), whose sum is σ = 60836594. Its totient is φ = 7031808.

The previous prime is 21097723. The next prime is 21097753. The reversal of 21097728 is 82779012.

It can be written as a sum of positive squares in only one way, i.e., 14379264 + 6718464 = 3792^2 + 2592^2 .

It is a super-2 number, since 2×21097728² = 890228253523968, which contains 22 as substring.

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 = 21097692 and 21097701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21097723) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2275 + ... + 6882.

Almost surely, 2^21097728 is an apocalyptic number.

It is an amenable number.

21097728 is an abundant number, since it is smaller than the sum of its proper divisors (39738866).

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

21097728 is an equidigital number, since it uses as much as digits as its factorization.

21097728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9179 (or 9162 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 21097728 is about 4593.2263170891. The cubic root of 21097728 is about 276.3197302868.

The spelling of 21097728 in words is "twenty-one million, ninety-seven thousand, seven hundred twenty-eight".