128391 has 4 divisors (see below), whose sum is σ = 171192. Its totient is φ = 85592.

The previous prime is 128389. The next prime is 128393. The reversal of 128391 is 193821.

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

It is an interprime number because it is at equal distance from previous prime (128389) and next prime (128393).

It is a cyclic number.

It is not a de Polignac number, because 128391 - 2¹ = 128389 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21396 + ... + 21401.

It is an arithmetic number, because the mean of its divisors is an integer number (42798).

2¹²⁸³⁹¹ is an apocalyptic number.

128391 is a deficient number, since it is larger than the sum of its proper divisors (42801).

128391 is an equidigital number, since it uses as much as digits as its factorization.

128391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42800.

The product of its digits is 432, while the sum is 24.

The square root of 128391 is about 358.3168988479. The cubic root of 128391 is about 50.4481053677.

The spelling of 128391 in words is "one hundred twenty-eight thousand, three hundred ninety-one".