28531821 has 4 divisors (see below), whose sum is σ = 38042432. Its totient is φ = 19021212.

The previous prime is 28531819. The next prime is 28531823. The reversal of 28531821 is 12813582.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (28531819) and next prime (28531823).

It is not a de Polignac number, because 28531821 - 2¹ = 28531819 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 (28531823) 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, 4755301 + ... + 4755306.

It is an arithmetic number, because the mean of its divisors is an integer number (9510608).

Almost surely, 2^28531821 is an apocalyptic number.

It is an amenable number.

28531821 is a deficient number, since it is larger than the sum of its proper divisors (9510611).

28531821 is an equidigital number, since it uses as much as digits as its factorization.

28531821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9510610.

The product of its digits is 3840, while the sum is 30.

The square root of 28531821 is about 5341.5186042922. The cubic root of 28531821 is about 305.5693780536.

The spelling of 28531821 in words is "twenty-eight million, five hundred thirty-one thousand, eight hundred twenty-one".