256686821 has 4 divisors (see below), whose sum is σ = 256736832. Its totient is φ = 256636812.

The previous prime is 256686803. The next prime is 256686839. The reversal of 256686821 is 128686652.

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.

It is an interprime number because it is at equal distance from previous prime (256686803) and next prime (256686839).

It is a cyclic number.

It is not a de Polignac number, because 256686821 - 2²⁶ = 189577957 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 (256686121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16295 + ... + 27908.

It is an arithmetic number, because the mean of its divisors is an integer number (64184208).

Almost surely, 2^256686821 is an apocalyptic number.

It is an amenable number.

256686821 is a deficient number, since it is larger than the sum of its proper divisors (50011).

256686821 is an equidigital number, since it uses as much as digits as its factorization.

256686821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50010.

The product of its digits is 276480, while the sum is 44.

The square root of 256686821 is about 16021.4487796828. The cubic root of 256686821 is about 635.5277576679.

The spelling of 256686821 in words is "two hundred fifty-six million, six hundred eighty-six thousand, eight hundred twenty-one".