231991 has 4 divisors (see below), whose sum is σ = 233800. Its totient is φ = 230184.

The previous prime is 231967. The next prime is 232003. The reversal of 231991 is 199132.

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

It is not a de Polignac number, because 231991 - 2⁹ = 231479 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (231901) 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, 696 + ... + 973.

It is an arithmetic number, because the mean of its divisors is an integer number (58450).

2²³¹⁹⁹¹ is an apocalyptic number.

231991 is a deficient number, since it is larger than the sum of its proper divisors (1809).

231991 is a wasteful number, since it uses less digits than its factorization.

231991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1808.

The product of its digits is 486, while the sum is 25.

The square root of 231991 is about 481.6544404446. The cubic root of 231991 is about 61.4455419387.

The spelling of 231991 in words is "two hundred thirty-one thousand, nine hundred ninety-one".