28569721 has 4 divisors (see below), whose sum is σ = 28591092. Its totient is φ = 28548352.

The previous prime is 28569719. The next prime is 28569757. The reversal of 28569721 is 12796582.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12796582 = 2 ⋅6398291.

It can be written as a sum of positive squares in 2 ways, for example, as 14402025 + 14167696 = 3795^2 + 3764^2 .

It is a cyclic number.

It is not a de Polignac number, because 28569721 - 2¹ = 28569719 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28563721) 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, 8536 + ... + 11401.

It is an arithmetic number, because the mean of its divisors is an integer number (7147773).

Almost surely, 2^28569721 is an apocalyptic number.

It is an amenable number.

28569721 is a deficient number, since it is larger than the sum of its proper divisors (21371).

28569721 is a wasteful number, since it uses less digits than its factorization.

28569721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21370.

The product of its digits is 60480, while the sum is 40.

The square root of 28569721 is about 5345.0651071806. The cubic root of 28569721 is about 305.7046183447.

The spelling of 28569721 in words is "twenty-eight million, five hundred sixty-nine thousand, seven hundred twenty-one".