688721618 has 24 divisors (see below), whose sum is σ = 1120540428. Its totient is φ = 315604512.

The previous prime is 688721617. The next prime is 688721647. The reversal of 688721618 is 816127886.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 688695049 + 26569 = 26243^2 + 163^2 .

It is not an unprimeable number, because it can be changed into a prime (688721611) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 690296 + ... + 691292.

Almost surely, 2^688721618 is an apocalyptic number.

688721618 is a deficient number, since it is larger than the sum of its proper divisors (431818810).

688721618 is a wasteful number, since it uses less digits than its factorization.

688721618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1338 (or 1175 counting only the distinct ones).

The product of its digits is 258048, while the sum is 47.

The square root of 688721618 is about 26243.5062062980. The cubic root of 688721618 is about 883.1095305174.

The spelling of 688721618 in words is "six hundred eighty-eight million, seven hundred twenty-one thousand, six hundred eighteen".