28731821 has 4 divisors (see below), whose sum is σ = 28743132. Its totient is φ = 28720512.

The previous prime is 28731809. The next prime is 28731877. The reversal of 28731821 is 12813782.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 21058921 + 7672900 = 4589^2 + 2770^2 .

It is a cyclic number.

It is not a de Polignac number, because 28731821 - 2⁶ = 28731757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28731881) 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, 125 + ... + 7581.

It is an arithmetic number, because the mean of its divisors is an integer number (7185783).

Almost surely, 2^28731821 is an apocalyptic number.

It is an amenable number.

28731821 is a deficient number, since it is larger than the sum of its proper divisors (11311).

28731821 is an equidigital number, since it uses as much as digits as its factorization.

28731821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11310.

The product of its digits is 5376, while the sum is 32.

The square root of 28731821 is about 5360.2071788318. The cubic root of 28731821 is about 306.2817012304.

The spelling of 28731821 in words is "twenty-eight million, seven hundred thirty-one thousand, eight hundred twenty-one".