21789728 has 12 divisors (see below), whose sum is σ = 42898590. Its totient is φ = 10894848.

The previous prime is 21789727. The next prime is 21789739. The reversal of 21789728 is 82798712.

It can be written as a sum of positive squares in only one way, i.e., 12475024 + 9314704 = 3532^2 + 3052^2 .

It is a Smith number, since the sum of its digits (44) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21789727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340433 + ... + 340496.

Almost surely, 2^21789728 is an apocalyptic number.

It is an amenable number.

21789728 is a deficient number, since it is larger than the sum of its proper divisors (21108862).

21789728 is an equidigital number, since it uses as much as digits as its factorization.

21789728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 680939 (or 680931 counting only the distinct ones).

The product of its digits is 112896, while the sum is 44.

The square root of 21789728 is about 4667.9468720199. The cubic root of 21789728 is about 279.3083609892.

The spelling of 21789728 in words is "twenty-one million, seven hundred eighty-nine thousand, seven hundred twenty-eight".