851991 has 16 divisors (see below), whose sum is σ = 1344000. Its totient is φ = 469728.

The previous prime is 851971. The next prime is 852011. The reversal of 851991 is 199158.

It is an interprime number because it is at equal distance from previous prime (851971) and next prime (852011).

It is not a de Polignac number, because 851991 - 2⁷ = 851863 is a prime.

851991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (851971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 91 + ... + 1308.

It is an arithmetic number, because the mean of its divisors is an integer number (84000).

2⁸⁵¹⁹⁹¹ is an apocalyptic number.

851991 is a deficient number, since it is larger than the sum of its proper divisors (492009).

851991 is a wasteful number, since it uses less digits than its factorization.

851991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1438.

The product of its digits is 3240, while the sum is 33.

The square root of 851991 is about 923.0335855211. The cubic root of 851991 is about 94.8007272639.

The spelling of 851991 in words is "eight hundred fifty-one thousand, nine hundred ninety-one".