256681 has 4 divisors (see below), whose sum is σ = 257872. Its totient is φ = 255492.

The previous prime is 256661. The next prime is 256687. The reversal of 256681 is 186652.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 256681 - 2⁹ = 256169 is a prime.

It is a super-2 number, since 2×256681² = 131770271522, which contains 22 as substring.

It is a Duffinian number.

It is a nialpdrome in base 4.

It is not an unprimeable number, because it can be changed into a prime (256687) 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, 171 + ... + 736.

It is an arithmetic number, because the mean of its divisors is an integer number (64468).

2²⁵⁶⁶⁸¹ is an apocalyptic number.

It is an amenable number.

256681 is a deficient number, since it is larger than the sum of its proper divisors (1191).

256681 is an equidigital number, since it uses as much as digits as its factorization.

256681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1190.

The product of its digits is 2880, while the sum is 28.

The square root of 256681 is about 506.6369508830. The cubic root of 256681 is about 63.5522953584.

The spelling of 256681 in words is "two hundred fifty-six thousand, six hundred eighty-one".