531991 has 6 divisors (see below), whose sum is σ = 553376. Its totient is φ = 510900.

The previous prime is 531989. The next prime is 531997. The reversal of 531991 is 199135.

It is not a de Polignac number, because 531991 - 2¹ = 531989 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 (531997) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3996 + ... + 4126.

2⁵³¹⁹⁹¹ is an apocalyptic number.

531991 is a deficient number, since it is larger than the sum of its proper divisors (21385).

531991 is an equidigital number, since it uses as much as digits as its factorization.

With its predecessor (531990) it forms a Ruth-Aaron pair, since the sum of their prime factors is the same (293).

531991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 293 (or 162 counting only the distinct ones).

The product of its digits is 1215, while the sum is 28.

The square root of 531991 is about 729.3771315307. The cubic root of 531991 is about 81.0279332608.

The spelling of 531991 in words is "five hundred thirty-one thousand, nine hundred ninety-one".