256681021 has 4 divisors (see below), whose sum is σ = 257132700. Its totient is φ = 256229344.

The previous prime is 256680979. The next prime is 256681043. The reversal of 256681021 is 120186652.

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 163558521 + 93122500 = 12789^2 + 9650^2 .

It is a cyclic number.

It is not a de Polignac number, because 256681021 - 2¹¹ = 256678973 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 (256681091) 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, 224986 + ... + 226123.

It is an arithmetic number, because the mean of its divisors is an integer number (64283175).

Almost surely, 2^256681021 is an apocalyptic number.

It is an amenable number.

256681021 is a deficient number, since it is larger than the sum of its proper divisors (451679).

256681021 is an equidigital number, since it uses as much as digits as its factorization.

256681021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 451678.

The product of its (nonzero) digits is 5760, while the sum is 31.

The square root of 256681021 is about 16021.2677713095. The cubic root of 256681021 is about 635.5229709155.

The spelling of 256681021 in words is "two hundred fifty-six million, six hundred eighty-one thousand, twenty-one".