256645 has 4 divisors (see below), whose sum is σ = 307980. Its totient is φ = 205312.

The previous prime is 256643. The next prime is 256651. The reversal of 256645 is 546652.

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 164836 + 91809 = 406^2 + 303^2 .

It is a cyclic number.

It is not a de Polignac number, because 256645 - 2¹ = 256643 is a prime.

256645 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 25660 + ... + 25669.

It is an arithmetic number, because the mean of its divisors is an integer number (76995).

2²⁵⁶⁶⁴⁵ is an apocalyptic number.

It is an amenable number.

256645 is a deficient number, since it is larger than the sum of its proper divisors (51335).

256645 is an equidigital number, since it uses as much as digits as its factorization.

256645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51334.

The product of its digits is 7200, while the sum is 28.

The square root of 256645 is about 506.6014212376. The cubic root of 256645 is about 63.5493241093.

It can be divided in two parts, 25 and 6645, that added together give a triangular number (6670 = T₁₁₅).

The spelling of 256645 in words is "two hundred fifty-six thousand, six hundred forty-five".