28812221 has 4 divisors (see below), whose sum is σ = 28850844. Its totient is φ = 28773600.

The previous prime is 28812209. The next prime is 28812247. The reversal of 28812221 is 12221882.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12221882 = 2 ⋅6110941.

It can be written as a sum of positive squares in 2 ways, for example, as 12924025 + 15888196 = 3595^2 + 3986^2 .

It is a cyclic number.

It is not a de Polignac number, because 28812221 - 2¹⁸ = 28550077 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28812521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18170 + ... + 19691.

It is an arithmetic number, because the mean of its divisors is an integer number (7212711).

Almost surely, 2^28812221 is an apocalyptic number.

It is an amenable number.

28812221 is a deficient number, since it is larger than the sum of its proper divisors (38623).

28812221 is an equidigital number, since it uses as much as digits as its factorization.

28812221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38622.

The product of its digits is 1024, while the sum is 26.

The square root of 28812221 is about 5367.7016496821. The cubic root of 28812221 is about 306.5671236205.

The spelling of 28812221 in words is "twenty-eight million, eight hundred twelve thousand, two hundred twenty-one".