28307021 has 4 divisors (see below), whose sum is σ = 28341600. Its totient is φ = 28272444.

The previous prime is 28307011. The next prime is 28307033. The reversal of 28307021 is 12070382.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12070382 = 2 ⋅6035191.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28307021 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 (28307011) 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, 16031 + ... + 17708.

It is an arithmetic number, because the mean of its divisors is an integer number (7085400).

Almost surely, 2^28307021 is an apocalyptic number.

It is an amenable number.

28307021 is a deficient number, since it is larger than the sum of its proper divisors (34579).

28307021 is an equidigital number, since it uses as much as digits as its factorization.

28307021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34578.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 28307021 is about 5320.4342867852. The cubic root of 28307021 is about 304.7647419910.

The spelling of 28307021 in words is "twenty-eight million, three hundred seven thousand, twenty-one".