28389721 has 4 divisors (see below), whose sum is σ = 28537012. Its totient is φ = 28242432.

The previous prime is 28389719. The next prime is 28389727. The reversal of 28389721 is 12798382.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18181696 + 10208025 = 4264^2 + 3195^2 .

It is a cyclic number.

It is not a de Polignac number, because 28389721 - 2¹ = 28389719 is a prime.

It is a super-3 number, since 3×28389721³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28389727) 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, 73356 + ... + 73741.

It is an arithmetic number, because the mean of its divisors is an integer number (7134253).

Almost surely, 2^28389721 is an apocalyptic number.

It is an amenable number.

28389721 is a deficient number, since it is larger than the sum of its proper divisors (147291).

28389721 is a wasteful number, since it uses less digits than its factorization.

28389721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 147290.

The product of its digits is 48384, while the sum is 40.

The square root of 28389721 is about 5328.2005405202. The cubic root of 28389721 is about 305.0612472181.

The spelling of 28389721 in words is "twenty-eight million, three hundred eighty-nine thousand, seven hundred twenty-one".