28011891 has 4 divisors (see below), whose sum is σ = 37349192. Its totient is φ = 18674592.

The previous prime is 28011857. The next prime is 28011901. The reversal of 28011891 is 19811082.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 28011891 - 2¹⁰ = 28010867 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28011811) 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, 4668646 + ... + 4668651.

It is an arithmetic number, because the mean of its divisors is an integer number (9337298).

Almost surely, 2^28011891 is an apocalyptic number.

28011891 is a deficient number, since it is larger than the sum of its proper divisors (9337301).

28011891 is an equidigital number, since it uses as much as digits as its factorization.

28011891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9337300.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 28011891 is about 5292.6260967501. The cubic root of 28011891 is about 303.7018769128.

The spelling of 28011891 in words is "twenty-eight million, eleven thousand, eight hundred ninety-one".