865991 has 8 divisors (see below), whose sum is σ = 996384. Its totient is φ = 737280.

The previous prime is 865979. The next prime is 865993. The reversal of 865991 is 199568.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 865991 - 2¹⁰ = 864967 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 (865993) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1031 + ... + 1671.

It is an arithmetic number, because the mean of its divisors is an integer number (124548).

2⁸⁶⁵⁹⁹¹ is an apocalyptic number.

865991 is a deficient number, since it is larger than the sum of its proper divisors (130393).

865991 is a wasteful number, since it uses less digits than its factorization.

865991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 841.

The product of its digits is 19440, while the sum is 38.

The square root of 865991 is about 930.5863742824. The cubic root of 865991 is about 95.3171670742.

The spelling of 865991 in words is "eight hundred sixty-five thousand, nine hundred ninety-one".