686808571355721 has 6 divisors (see below), whose sum is σ = 992056825291610. Its totient is φ = 457872380903808.

The previous prime is 686808571355707. The next prime is 686808571355759. The reversal of 686808571355721 is 127553175808686.

686808571355721 is a `hidden beast` number, since 6 + 8 + 6 + 8 + 0 + 8 + 57 + 13 + 557 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 474690319437321 + 212118251918400 = 21787389^2 + 14564280^2 .

It is not a de Polignac number, because 686808571355721 - 2⁷ = 686808571355593 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 686808571355721.

It is not an unprimeable number, because it can be changed into a prime (686808571355791) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 38156031741976 + ... + 38156031741993.

Almost surely, 2^{686808571355721} is an apocalyptic number.

It is an amenable number.

686808571355721 is a deficient number, since it is larger than the sum of its proper divisors (305248253935889).

686808571355721 is a wasteful number, since it uses less digits than its factorization.

686808571355721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76312063483975 (or 76312063483972 counting only the distinct ones).

The product of its (nonzero) digits is 677376000, while the sum is 72.

The spelling of 686808571355721 in words is "six hundred eighty-six trillion, eight hundred eight billion, five hundred seventy-one million, three hundred fifty-five thousand, seven hundred twenty-one".