256565640 has 64 divisors (see below), whose sum is σ = 778377600. Its totient is φ = 67645952.

The previous prime is 256565629. The next prime is 256565677. The reversal of 256565640 is 46565652.

It is a happy number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1332 + ... + 22691.

It is an arithmetic number, because the mean of its divisors is an integer number (12162150).

Almost surely, 2^256565640 is an apocalyptic number.

256565640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 256565640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (389188800).

256565640 is an abundant number, since it is smaller than the sum of its proper divisors (521811960).

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

256565640 is a wasteful number, since it uses less digits than its factorization.

256565640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24126 (or 24122 counting only the distinct ones).

The product of its (nonzero) digits is 216000, while the sum is 39.

The square root of 256565640 is about 16017.6664967154. Note that the first 3 decimals coincide. The cubic root of 256565640 is about 635.4277317408.

The spelling of 256565640 in words is "two hundred fifty-six million, five hundred sixty-five thousand, six hundred forty".