688686821 has 2 divisors, whose sum is σ = 688686822. Its totient is φ = 688686820.

The previous prime is 688686709. The next prime is 688686827. The reversal of 688686821 is 128686886.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 602457025 + 86229796 = 24545^2 + 9286^2 .

It is a cyclic number.

It is not a de Polignac number, because 688686821 - 2¹⁸ = 688424677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (688686827) 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 as a sum of consecutive naturals, namely, 344343410 + 344343411.

It is an arithmetic number, because the mean of its divisors is an integer number (344343411).

Almost surely, 2^688686821 is an apocalyptic number.

It is an amenable number.

688686821 is a deficient number, since it is larger than the sum of its proper divisors (1).

688686821 is an equidigital number, since it uses as much as digits as its factorization.

688686821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1769472, while the sum is 53.

The square root of 688686821 is about 26242.8432339181. The cubic root of 688686821 is about 883.0946575126.

The spelling of 688686821 in words is "six hundred eighty-eight million, six hundred eighty-six thousand, eight hundred twenty-one".