686730721 has 4 divisors (see below), whose sum is σ = 691743492. Its totient is φ = 681717952.

The previous prime is 686730679. The next prime is 686730787. The reversal of 686730721 is 127037686.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 587529121 + 99201600 = 24239^2 + 9960^2 .

It is a cyclic number.

It is not a de Polignac number, because 686730721 - 2¹⁵ = 686697953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (686730791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2506180 + ... + 2506453.

It is an arithmetic number, because the mean of its divisors is an integer number (172935873).

Almost surely, 2^686730721 is an apocalyptic number.

It is an amenable number.

686730721 is a deficient number, since it is larger than the sum of its proper divisors (5012771).

686730721 is a wasteful number, since it uses less digits than its factorization.

686730721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5012770.

The product of its (nonzero) digits is 84672, while the sum is 40.

The square root of 686730721 is about 26205.5475233776. The cubic root of 686730721 is about 882.2577703255.

The spelling of 686730721 in words is "six hundred eighty-six million, seven hundred thirty thousand, seven hundred twenty-one".