28705991 has 4 divisors (see below), whose sum is σ = 28766400. Its totient is φ = 28645584.

The previous prime is 28705961. The next prime is 28706003. The reversal of 28705991 is 19950782.

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 28705991 - 2⁶ = 28705927 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 (28705921) 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, 29486 + ... + 30443.

It is an arithmetic number, because the mean of its divisors is an integer number (7191600).

Almost surely, 2^28705991 is an apocalyptic number.

28705991 is a deficient number, since it is larger than the sum of its proper divisors (60409).

28705991 is an equidigital number, since it uses as much as digits as its factorization.

28705991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60408.

The product of its (nonzero) digits is 45360, while the sum is 41.

The square root of 28705991 is about 5357.7972152742. The cubic root of 28705991 is about 306.1898909656.

The spelling of 28705991 in words is "twenty-eight million, seven hundred five thousand, nine hundred ninety-one".