688628981 has 2 divisors, whose sum is σ = 688628982. Its totient is φ = 688628980.

The previous prime is 688628933. The next prime is 688628987. The reversal of 688628981 is 189826886.

688628981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 558896881 + 129732100 = 23641^2 + 11390^2 .

It is a cyclic number.

It is not a de Polignac number, because 688628981 - 2¹⁸ = 688366837 is a prime.

It is a super-2 number, since 2×688628981² = 948419746946196722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (688628987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 344314490 + 344314491.

It is an arithmetic number, because the mean of its divisors is an integer number (344314491).

Almost surely, 2^688628981 is an apocalyptic number.

It is an amenable number.

688628981 is a deficient number, since it is larger than the sum of its proper divisors (1).

688628981 is an equidigital number, since it uses as much as digits as its factorization.

688628981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2654208, while the sum is 56.

The square root of 688628981 is about 26241.7411960411. The cubic root of 688628981 is about 883.0699343131.

The spelling of 688628981 in words is "six hundred eighty-eight million, six hundred twenty-eight thousand, nine hundred eighty-one".