688989721 has 4 divisors (see below), whose sum is σ = 787416832. Its totient is φ = 590562612.

The previous prime is 688989703. The next prime is 688989733. The reversal of 688989721 is 127989886.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 688989721 - 2⁵ = 688989689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (688989701) by changing a digit.

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, 49213545 + ... + 49213558.

It is an arithmetic number, because the mean of its divisors is an integer number (196854208).

Almost surely, 2^688989721 is an apocalyptic number.

It is an amenable number.

688989721 is a deficient number, since it is larger than the sum of its proper divisors (98427111).

688989721 is an equidigital number, since it uses as much as digits as its factorization.

688989721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 98427110.

The product of its digits is 3483648, while the sum is 58.

The square root of 688989721 is about 26248.6136967269. The cubic root of 688989721 is about 883.2241068536.

The spelling of 688989721 in words is "six hundred eighty-eight million, nine hundred eighty-nine thousand, seven hundred twenty-one".