28191881 has 4 divisors (see below), whose sum is σ = 28208532. Its totient is φ = 28175232.

The previous prime is 28191853. The next prime is 28191893. The reversal of 28191881 is 18819182.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18819182 = 2 ⋅9409591.

It can be written as a sum of positive squares in 2 ways, for example, as 24255625 + 3936256 = 4925^2 + 1984^2 .

It is a cyclic number.

It is not a de Polignac number, because 28191881 - 2¹⁰ = 28190857 is a prime.

It is a super-2 number, since 2×28191881² = 1589564308636322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28191281) 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, 5456 + ... + 9281.

It is an arithmetic number, because the mean of its divisors is an integer number (7052133).

Almost surely, 2^28191881 is an apocalyptic number.

It is an amenable number.

28191881 is a deficient number, since it is larger than the sum of its proper divisors (16651).

28191881 is a wasteful number, since it uses less digits than its factorization.

28191881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16650.

The product of its digits is 9216, while the sum is 38.

The square root of 28191881 is about 5309.6027158348. The cubic root of 28191881 is about 304.3509659916.

The spelling of 28191881 in words is "twenty-eight million, one hundred ninety-one thousand, eight hundred eighty-one".