• 865 can be written using four 4's:

See also 113.

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865 has 4 divisors (see below), whose sum is σ = 1044. Its totient is φ = 688.

The previous prime is 863. The next prime is 877. The reversal of 865 is 568.

865 is nontrivially palindromic in base 11.

865 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 can be written as a sum of positive squares in 2 ways, for example, as 576 + 289 = 24^2 + 17^2 .

It is a cyclic number.

It is not a de Polignac number, because 865 - 2¹ = 863 is a prime.

It is a Duffinian number.

865 is an undulating number in base 11.

It is a plaindrome in base 7 and base 14.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 82 + ... + 91.

It is an arithmetic number, because the mean of its divisors is an integer number (261).

It is a Proth number, since it is equal to 27 ⋅ 2⁵ + 1 and 27 < 2⁵.

2⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

865 is a deficient number, since it is larger than the sum of its proper divisors (179).

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

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

The sum of its prime factors is 178.

The product of its digits is 240, while the sum is 19.

The square root of 865 is about 29.4108823397. The cubic root of 865 is about 9.5280794345.

Subtracting from 865 its product of digits (240), we obtain a 4-th power (625 = 5⁴).

It can be divided in two parts, 86 and 5, that added together give a triangular number (91 = T₁₃).

The spelling of 865 in words is "eight hundred sixty-five", and thus it is an aban number and an oban number.