686559730921 has 27 divisors (see below), whose sum is σ = 710224504311. Its totient is φ = 663679902864.

The previous prime is 686559730919. The next prime is 686559731021. The reversal of 686559730921 is 129037955686.

The square root of 686559730921 is 828589.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 80435199321 + 606124531600 = 283611^2 + 778540^2 .

It is not a de Polignac number, because 686559730921 - 2¹ = 686559730919 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 686559730921.

It is not an unprimeable number, because it can be changed into a prime (686559736921) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 4607783355 + ... + 4607783503.

Almost surely, 2^686559730921 is an apocalyptic number.

686559730921 is the 828589-th square number.

686559730921 is the 414295-th centered octagonal number.

It is an amenable number.

686559730921 is a deficient number, since it is larger than the sum of its proper divisors (23664773390).

686559730921 is an frugal number, since it uses more digits than its factorization.

686559730921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 598 (or 299 counting only the distinct ones).

The product of its (nonzero) digits is 24494400, while the sum is 61.

The spelling of 686559730921 in words is "six hundred eighty-six billion, five hundred fifty-nine million, seven hundred thirty thousand, nine hundred twenty-one".