28565721 has 12 divisors (see below), whose sum is σ = 43433520. Its totient is φ = 18041400.

The previous prime is 28565687. The next prime is 28565723. The reversal of 28565721 is 12756582.

It is a happy number.

28565721 is a `hidden beast` number, since 2 + 85 + 6 + 572 + 1 = 666.

It is not a de Polignac number, because 28565721 - 2⁹ = 28565209 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (28565723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 83355 + ... + 83696.

It is an arithmetic number, because the mean of its divisors is an integer number (3619460).

Almost surely, 2^28565721 is an apocalyptic number.

It is an amenable number.

28565721 is a deficient number, since it is larger than the sum of its proper divisors (14867799).

28565721 is a wasteful number, since it uses less digits than its factorization.

28565721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167076 (or 167073 counting only the distinct ones).

The product of its digits is 33600, while the sum is 36.

The square root of 28565721 is about 5344.6909171626. The cubic root of 28565721 is about 305.6903506106.

The spelling of 28565721 in words is "twenty-eight million, five hundred sixty-five thousand, seven hundred twenty-one".