28740821 has 4 divisors (see below), whose sum is σ = 29212044. Its totient is φ = 28269600.

The previous prime is 28740799. The next prime is 28740851. The reversal of 28740821 is 12804782.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12804782 = 2 ⋅6402391.

It can be written as a sum of positive squares in 2 ways, for example, as 15132100 + 13608721 = 3890^2 + 3689^2 .

It is a cyclic number.

It is not a de Polignac number, because 28740821 - 2¹⁰ = 28739797 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 (28740851) 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, 235520 + ... + 235641.

It is an arithmetic number, because the mean of its divisors is an integer number (7303011).

Almost surely, 2^28740821 is an apocalyptic number.

It is an amenable number.

28740821 is a deficient number, since it is larger than the sum of its proper divisors (471223).

28740821 is an equidigital number, since it uses as much as digits as its factorization.

28740821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 471222.

The product of its (nonzero) digits is 7168, while the sum is 32.

The square root of 28740821 is about 5361.0466328880. The cubic root of 28740821 is about 306.3136779429.

The spelling of 28740821 in words is "twenty-eight million, seven hundred forty thousand, eight hundred twenty-one".