23991 has 8 divisors (see below), whose sum is σ = 34944. Its totient is φ = 14520.

The previous prime is 23981. The next prime is 23993. The reversal of 23991 is 19932.

It is a happy number.

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

It is not a de Polignac number, because 23991 - 2¹¹ = 21943 is a prime.

23991 is a lucky number.

It is a plaindrome in base 8.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (23993) 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 7 ways as a sum of consecutive naturals, for example, 331 + ... + 396.

It is an arithmetic number, because the mean of its divisors is an integer number (4368).

2²³⁹⁹¹ is an apocalyptic number.

23991 is a deficient number, since it is larger than the sum of its proper divisors (10953).

23991 is a wasteful number, since it uses less digits than its factorization.

23991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 741.

The product of its digits is 486, while the sum is 24.

The square root of 23991 is about 154.8902837495. The cubic root of 23991 is about 28.8413853314.

It can be divided in two parts, 2 and 3991, that added together give a palindrome (3993).

The spelling of 23991 in words is "twenty-three thousand, nine hundred ninety-one".