687929821 has 2 divisors, whose sum is σ = 687929822. Its totient is φ = 687929820.

The previous prime is 687929819. The next prime is 687929843. The reversal of 687929821 is 128929786.

687929821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 661004100 + 26925721 = 25710^2 + 5189^2 .

It is a cyclic number.

It is not a de Polignac number, because 687929821 - 2¹ = 687929819 is a prime.

Together with 687929819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (687929521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343964910 + 343964911.

It is an arithmetic number, because the mean of its divisors is an integer number (343964911).

Almost surely, 2^687929821 is an apocalyptic number.

It is an amenable number.

687929821 is a deficient number, since it is larger than the sum of its proper divisors (1).

687929821 is an equidigital number, since it uses as much as digits as its factorization.

687929821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 870912, while the sum is 52.

The square root of 687929821 is about 26228.4162884456. The cubic root of 687929821 is about 882.7709749509.

The spelling of 687929821 in words is "six hundred eighty-seven million, nine hundred twenty-nine thousand, eight hundred twenty-one".