861891 has 4 divisors (see below), whose sum is σ = 1149192. Its totient is φ = 574592.

The previous prime is 861881. The next prime is 861899. The reversal of 861891 is 198168.

861891 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 861891 - 2¹⁵ = 829123 is a prime.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (861899) 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, 143646 + ... + 143651.

It is an arithmetic number, because the mean of its divisors is an integer number (287298).

2⁸⁶¹⁸⁹¹ is an apocalyptic number.

861891 is a deficient number, since it is larger than the sum of its proper divisors (287301).

861891 is a wasteful number, since it uses less digits than its factorization.

861891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 287300.

The product of its digits is 3456, while the sum is 33.

The square root of 861891 is about 928.3808485745. The cubic root of 861891 is about 95.1665039398.

The spelling of 861891 in words is "eight hundred sixty-one thousand, eight hundred ninety-one".