863991 has 12 divisors (see below), whose sum is σ = 1321632. Its totient is φ = 542016.

The previous prime is 863983. The next prime is 864007. The reversal of 863991 is 199368.

It is not a de Polignac number, because 863991 - 2³ = 863983 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

863991 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 863991.

It is not an unprimeable number, because it can be changed into a prime (863921) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2671 + ... + 2976.

It is an arithmetic number, because the mean of its divisors is an integer number (110136).

2⁸⁶³⁹⁹¹ is an apocalyptic number.

863991 is a deficient number, since it is larger than the sum of its proper divisors (457641).

863991 is a wasteful number, since it uses less digits than its factorization.

863991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5670 (or 5667 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 863991 is about 929.5111618480. The cubic root of 863991 is about 95.2437324084.

Subtracting from 863991 its sum of digits (36), we obtain a triangular number (863955 = T₁₃₁₄).

The spelling of 863991 in words is "eight hundred sixty-three thousand, nine hundred ninety-one".