256805 has 4 divisors (see below), whose sum is σ = 308172. Its totient is φ = 205440.

The previous prime is 256801. The next prime is 256813. The reversal of 256805 is 508652.

256805 = T₃₁₈ + T₃₁₉ + ... + T₃₂₂.

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 42436 + 214369 = 206^2 + 463^2 .

It is not a de Polignac number, because 256805 - 2² = 256801 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 (256801) 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 3 ways as a sum of consecutive naturals, for example, 25676 + ... + 25685.

It is an arithmetic number, because the mean of its divisors is an integer number (77043).

2²⁵⁶⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

256805 is a deficient number, since it is larger than the sum of its proper divisors (51367).

256805 is an equidigital number, since it uses as much as digits as its factorization.

256805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51366.

The product of its (nonzero) digits is 2400, while the sum is 26.

The square root of 256805 is about 506.7593117053. The cubic root of 256805 is about 63.5625275350.

The spelling of 256805 in words is "two hundred fifty-six thousand, eight hundred five".