688942781 has 2 divisors, whose sum is σ = 688942782. Its totient is φ = 688942780.

The previous prime is 688942739. The next prime is 688942811. The reversal of 688942781 is 187249886.

It is a happy number.

688942781 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., 671587225 + 17355556 = 25915^2 + 4166^2 .

It is a cyclic number.

It is not a de Polignac number, because 688942781 - 2¹⁸ = 688680637 is a prime.

It is a super-2 number, since 2×688942781² = 949284310984027922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (688942711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 344471390 + 344471391.

It is an arithmetic number, because the mean of its divisors is an integer number (344471391).

Almost surely, 2^688942781 is an apocalyptic number.

It is an amenable number.

688942781 is a deficient number, since it is larger than the sum of its proper divisors (1).

688942781 is an equidigital number, since it uses as much as digits as its factorization.

688942781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1548288, while the sum is 53.

The square root of 688942781 is about 26247.7195390381. The cubic root of 688942781 is about 883.2040487502.

The spelling of 688942781 in words is "six hundred eighty-eight million, nine hundred forty-two thousand, seven hundred eighty-one".