491991 has 4 divisors (see below), whose sum is σ = 655992. Its totient is φ = 327992.

The previous prime is 491983. The next prime is 492007. The reversal of 491991 is 199194.

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 491991 - 2³ = 491983 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (491951) 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 3 ways as a sum of consecutive naturals, for example, 81996 + ... + 82001.

It is an arithmetic number, because the mean of its divisors is an integer number (163998).

2⁴⁹¹⁹⁹¹ is an apocalyptic number.

491991 is a deficient number, since it is larger than the sum of its proper divisors (164001).

491991 is a wasteful number, since it uses less digits than its factorization.

491991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 164000.

The product of its digits is 2916, while the sum is 33.

The square root of 491991 is about 701.4207011487. The cubic root of 491991 is about 78.9439863580.

The spelling of 491991 in words is "four hundred ninety-one thousand, nine hundred ninety-one".