256905 has 32 divisors (see below), whose sum is σ = 501120. Its totient is φ = 123840.

The previous prime is 256903. The next prime is 256931. The reversal of 256905 is 509652.

It is not a de Polignac number, because 256905 - 2¹ = 256903 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256901) 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 31 ways as a sum of consecutive naturals, for example, 1399 + ... + 1571.

It is an arithmetic number, because the mean of its divisors is an integer number (15660).

2²⁵⁶⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

256905 is a deficient number, since it is larger than the sum of its proper divisors (244215).

256905 is a wasteful number, since it uses less digits than its factorization.

256905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 198 (or 192 counting only the distinct ones).

The product of its (nonzero) digits is 2700, while the sum is 27.

The square root of 256905 is about 506.8579682712. The cubic root of 256905 is about 63.5707768914.

The spelling of 256905 in words is "two hundred fifty-six thousand, nine hundred five".