256409 has 8 divisors (see below), whose sum is σ = 269280. Its totient is φ = 243936.

The previous prime is 256393. The next prime is 256423. The reversal of 256409 is 904652.

256409 = T₈₇ + T₈₈ + ... + T₁₂₉.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 256409 - 2⁴ = 256393 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (256469) 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 7 ways as a sum of consecutive naturals, for example, 2837 + ... + 2925.

It is an arithmetic number, because the mean of its divisors is an integer number (33660).

2²⁵⁶⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

256409 is a deficient number, since it is larger than the sum of its proper divisors (12871).

256409 is an equidigital number, since it uses as much as digits as its factorization.

256409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 199.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 256409 is about 506.3684429346. The cubic root of 256409 is about 63.5298390360.

The spelling of 256409 in words is "two hundred fifty-six thousand, four hundred nine".