311991 has 4 divisors (see below), whose sum is σ = 415992. Its totient is φ = 207992.

The previous prime is 311981. The next prime is 312007. The reversal of 311991 is 199113.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-311991 is a prime.

It is a D-number.

311991 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 311991.

It is not an unprimeable number, because it can be changed into a prime (311951) 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, 51996 + ... + 52001.

It is an arithmetic number, because the mean of its divisors is an integer number (103998).

2³¹¹⁹⁹¹ is an apocalyptic number.

311991 is a deficient number, since it is larger than the sum of its proper divisors (104001).

311991 is a wasteful number, since it uses less digits than its factorization.

311991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104000.

The product of its digits is 243, while the sum is 24.

The square root of 311991 is about 558.5615454003. The cubic root of 311991 is about 67.8235766980.

The spelling of 311991 in words is "three hundred eleven thousand, nine hundred ninety-one".