28891991 has 4 divisors (see below), whose sum is σ = 28974192. Its totient is φ = 28809792.

The previous prime is 28891987. The next prime is 28891999. The reversal of 28891991 is 19919882.

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

It is a cyclic number.

It is not a de Polignac number, because 28891991 - 2² = 28891987 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 (28891999) 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, 40571 + ... + 41276.

It is an arithmetic number, because the mean of its divisors is an integer number (7243548).

Almost surely, 2^28891991 is an apocalyptic number.

28891991 is a deficient number, since it is larger than the sum of its proper divisors (82201).

28891991 is an equidigital number, since it uses as much as digits as its factorization.

28891991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82200.

The product of its digits is 93312, while the sum is 47.

The square root of 28891991 is about 5375.1270682655. The cubic root of 28891991 is about 306.8497852197.

The spelling of 28891991 in words is "twenty-eight million, eight hundred ninety-one thousand, nine hundred ninety-one".