256665 has 16 divisors (see below), whose sum is σ = 418176. Its totient is φ = 134400.

The previous prime is 256661. The next prime is 256687. The reversal of 256665 is 566652.

It is not a de Polignac number, because 256665 - 2² = 256661 is a prime.

256665 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (256661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 945 + ... + 1185.

It is an arithmetic number, because the mean of its divisors is an integer number (26136).

2²⁵⁶⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

256665 is a deficient number, since it is larger than the sum of its proper divisors (161511).

256665 is a wasteful number, since it uses less digits than its factorization.

256665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 320.

The product of its digits is 10800, while the sum is 30.

The square root of 256665 is about 506.6211602371. The cubic root of 256665 is about 63.5509748375.

The spelling of 256665 in words is "two hundred fifty-six thousand, six hundred sixty-five".