28091891 has 4 divisors (see below), whose sum is σ = 28103784. Its totient is φ = 28080000.

The previous prime is 28091881. The next prime is 28091893. The reversal of 28091891 is 19819082.

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 is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28091891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28091893) 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, 1070 + ... + 7571.

It is an arithmetic number, because the mean of its divisors is an integer number (7025946).

Almost surely, 2^28091891 is an apocalyptic number.

28091891 is a deficient number, since it is larger than the sum of its proper divisors (11893).

28091891 is an equidigital number, since it uses as much as digits as its factorization.

28091891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11892.

The product of its (nonzero) digits is 10368, while the sum is 38.

The square root of 28091891 is about 5300.1783932241. The cubic root of 28091891 is about 303.9907192169.

It can be divided in two parts, 28091 and 891, that added together give a palindrome (28982).

The spelling of 28091891 in words is "twenty-eight million, ninety-one thousand, eight hundred ninety-one".