331991 has 4 divisors (see below), whose sum is σ = 362184. Its totient is φ = 301800.

The previous prime is 331973. The next prime is 331997. The reversal of 331991 is 199133.

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

It is a cyclic number.

It is not a de Polignac number, because 331991 - 2¹⁸ = 69847 is a prime.

It is a super-2 number, since 2×331991² = 220436048162, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 331991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (331997) 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, 15080 + ... + 15101.

It is an arithmetic number, because the mean of its divisors is an integer number (90546).

2³³¹⁹⁹¹ is an apocalyptic number.

331991 is a deficient number, since it is larger than the sum of its proper divisors (30193).

331991 is a wasteful number, since it uses less digits than its factorization.

331991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30192.

The product of its digits is 729, while the sum is 26.

The square root of 331991 is about 576.1866017186. The cubic root of 331991 is about 69.2429300258.

It can be divided in two parts, 33 and 1991, that multiplied together give a triangular number (65703 = T₃₆₂).

The spelling of 331991 in words is "three hundred thirty-one thousand, nine hundred ninety-one".