521991 has 8 divisors (see below), whose sum is σ = 773360. Its totient is φ = 347976.

The previous prime is 521981. The next prime is 521993. The reversal of 521991 is 199125.

It is a happy number.

521991 is digitally balanced in base 7, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 521991 - 2¹⁰ = 520967 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 19333 = 521991 / (5 + 2 + 1 + 9 + 9 + 1).

It is a Duffinian number.

521991 is strictly pandigital in base 7.

It is a nialpdrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9640 + ... + 9693.

It is an arithmetic number, because the mean of its divisors is an integer number (96670).

2⁵²¹⁹⁹¹ is an apocalyptic number.

521991 is a deficient number, since it is larger than the sum of its proper divisors (251369).

521991 is a wasteful number, since it uses less digits than its factorization.

521991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19342 (or 19336 counting only the distinct ones).

The product of its digits is 810, while the sum is 27.

The square root of 521991 is about 722.4894462897. The cubic root of 521991 is about 80.5170160652.

The spelling of 521991 in words is "five hundred twenty-one thousand, nine hundred ninety-one".