256640 has 32 divisors (see below), whose sum is σ = 615060. Its totient is φ = 102400.

The previous prime is 256639. The next prime is 256643. The reversal of 256640 is 46652.

It can be written as a sum of positive squares in 2 ways, for example, as 238144 + 18496 = 488^2 + 136^2 .

It is a tau number, because it is divible by the number of its divisors (32).

It is a nialpdrome in base 4 and base 8.

It is a zygodrome in base 4.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 256640.

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, 440 + ... + 840.

2²⁵⁶⁶⁴⁰ is an apocalyptic number.

256640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 256640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (307530).

256640 is an abundant number, since it is smaller than the sum of its proper divisors (358420).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

256640 is an equidigital number, since it uses as much as digits as its factorization.

256640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 420 (or 408 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 23.

The square root of 256640 is about 506.5964863676. The cubic root of 256640 is about 63.5489114138.

The spelling of 256640 in words is "two hundred fifty-six thousand, six hundred forty".