668555865 has 24 divisors (see below), whose sum is σ = 1170311688. Its totient is φ = 353030400.

The previous prime is 668555863. The next prime is 668555887. The reversal of 668555865 is 568555866.

668555865 is a `hidden beast` number, since 6 + 6 + 8 + 55 + 586 + 5 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 405337689 + 263218176 = 20133^2 + 16224^2 .

It is not a de Polignac number, because 668555865 - 2¹ = 668555863 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (668555861) 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 23 ways as a sum of consecutive naturals, for example, 69004 + ... + 78093.

It is an arithmetic number, because the mean of its divisors is an integer number (48762987).

Almost surely, 2^668555865 is an apocalyptic number.

It is an amenable number.

668555865 is a deficient number, since it is larger than the sum of its proper divisors (501755823).

668555865 is a wasteful number, since it uses less digits than its factorization.

668555865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147209 (or 147206 counting only the distinct ones).

The product of its digits is 8640000, while the sum is 54.

The square root of 668555865 is about 25856.4472617566. The cubic root of 668555865 is about 874.4048698726.

Subtracting from 668555865 its reverse (568555866), we obtain a palindrome (99999999).

The spelling of 668555865 in words is "six hundred sixty-eight million, five hundred fifty-five thousand, eight hundred sixty-five".