256388861 has 4 divisors (see below), whose sum is σ = 256422300. Its totient is φ = 256355424.

The previous prime is 256388851. The next prime is 256388893. The reversal of 256388861 is 168883652.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 62900761 + 193488100 = 7931^2 + 13910^2 .

It is a cyclic number.

It is not a de Polignac number, because 256388861 - 2¹⁴ = 256372477 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 (256388801) 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, 1145 + ... + 22673.

It is an arithmetic number, because the mean of its divisors is an integer number (64105575).

Almost surely, 2^256388861 is an apocalyptic number.

It is an amenable number.

256388861 is a deficient number, since it is larger than the sum of its proper divisors (33439).

256388861 is a wasteful number, since it uses less digits than its factorization.

256388861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33438.

The product of its digits is 552960, while the sum is 47.

The square root of 256388861 is about 16012.1472951007. The cubic root of 256388861 is about 635.2817572861.

The spelling of 256388861 in words is "two hundred fifty-six million, three hundred eighty-eight thousand, eight hundred sixty-one".