256561664 has 40 divisors (see below), whose sum is σ = 519192960. Its totient is φ = 126637056.

The previous prime is 256561651. The next prime is 256561687. The reversal of 256561664 is 466165652.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 37277 + ... + 43619.

It is an arithmetic number, because the mean of its divisors is an integer number (12979824).

Almost surely, 2^256561664 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 256561664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (259596480).

256561664 is an abundant number, since it is smaller than the sum of its proper divisors (262631296).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

256561664 is an frugal number, since it uses more digits than its factorization.

256561664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6440 (or 6424 counting only the distinct ones).

The product of its digits is 259200, while the sum is 41.

The square root of 256561664 is about 16017.5423832747. The cubic root of 256561664 is about 635.4244493141.

The spelling of 256561664 in words is "two hundred fifty-six million, five hundred sixty-one thousand, six hundred sixty-four".