28684721 has 4 divisors (see below), whose sum is σ = 30891252. Its totient is φ = 26478192.

The previous prime is 28684709. The next prime is 28684727. The reversal of 28684721 is 12748682.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12748682 = 2 ⋅6374341.

It can be written as a sum of positive squares in 2 ways, for example, as 1852321 + 26832400 = 1361^2 + 5180^2 .

It is not a de Polignac number, because 28684721 - 2¹⁴ = 28668337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28684727) 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, 1103246 + ... + 1103271.

It is an arithmetic number, because the mean of its divisors is an integer number (7722813).

Almost surely, 2^28684721 is an apocalyptic number.

It is an amenable number.

28684721 is a deficient number, since it is larger than the sum of its proper divisors (2206531).

28684721 is a wasteful number, since it uses less digits than its factorization.

28684721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2206530.

The product of its digits is 43008, while the sum is 38.

The square root of 28684721 is about 5355.8118899005. The cubic root of 28684721 is about 306.1142474274.

The spelling of 28684721 in words is "twenty-eight million, six hundred eighty-four thousand, seven hundred twenty-one".