28139891 has 4 divisors (see below), whose sum is σ = 30304512. Its totient is φ = 25975272.

The previous prime is 28139863. The next prime is 28139897. The reversal of 28139891 is 19893182.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19893182 = 2 ⋅9946591.

It is a cyclic number.

It is not a de Polignac number, because 28139891 - 2¹⁴ = 28123507 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28139897) 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, 1082291 + ... + 1082316.

It is an arithmetic number, because the mean of its divisors is an integer number (7576128).

Almost surely, 2^28139891 is an apocalyptic number.

28139891 is a deficient number, since it is larger than the sum of its proper divisors (2164621).

28139891 is a wasteful number, since it uses less digits than its factorization.

28139891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2164620.

The product of its digits is 31104, while the sum is 41.

The square root of 28139891 is about 5304.7046100608. The cubic root of 28139891 is about 304.1637614618.

The spelling of 28139891 in words is "twenty-eight million, one hundred thirty-nine thousand, eight hundred ninety-one".