256665221 has 4 divisors (see below), whose sum is σ = 256787244. Its totient is φ = 256543200.

The previous prime is 256665217. The next prime is 256665223. The reversal of 256665221 is 122566652.

256665221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 236728996 + 19936225 = 15386^2 + 4465^2 .

It is a cyclic number.

It is not a de Polignac number, because 256665221 - 2² = 256665217 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 (256665223) 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, 57800 + ... + 62081.

It is an arithmetic number, because the mean of its divisors is an integer number (64196811).

Almost surely, 2^256665221 is an apocalyptic number.

It is an amenable number.

256665221 is a deficient number, since it is larger than the sum of its proper divisors (122023).

256665221 is a wasteful number, since it uses less digits than its factorization.

256665221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 122022.

The product of its digits is 43200, while the sum is 35.

The square root of 256665221 is about 16020.7746691600. The cubic root of 256665221 is about 635.5099307760.

The spelling of 256665221 in words is "two hundred fifty-six million, six hundred sixty-five thousand, two hundred twenty-one".