25991 has 8 divisors (see below), whose sum is σ = 30720. Its totient is φ = 21528.

The previous prime is 25981. The next prime is 25997. The reversal of 25991 is 19952.

25991 = 23³ + 24³.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 25991 - 2¹⁰ = 24967 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 25991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (25997) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 290 + ... + 368.

It is an arithmetic number, because the mean of its divisors is an integer number (3840).

2²⁵⁹⁹¹ is an apocalyptic number.

25991 is a deficient number, since it is larger than the sum of its proper divisors (4729).

25991 is an equidigital number, since it uses as much as digits as its factorization.

25991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133.

The product of its digits is 810, while the sum is 26.

The square root of 25991 is about 161.2172447352. The cubic root of 25991 is about 29.6215420249.

The spelling of 25991 in words is "twenty-five thousand, nine hundred ninety-one".