686561 has 4 divisors (see below), whose sum is σ = 691092. Its totient is φ = 682032.

The previous prime is 686551. The next prime is 686563. The reversal of 686561 is 165686.

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 295936 + 390625 = 544^2 + 625^2 .

It is a cyclic number.

It is not a de Polignac number, because 686561 - 2¹⁰ = 685537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (686563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2030 + ... + 2343.

It is an arithmetic number, because the mean of its divisors is an integer number (172773).

2⁶⁸⁶⁵⁶¹ is an apocalyptic number.

It is an amenable number.

686561 is a deficient number, since it is larger than the sum of its proper divisors (4531).

686561 is a wasteful number, since it uses less digits than its factorization.

686561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4530.

The product of its digits is 8640, while the sum is 32.

The square root of 686561 is about 828.5897658069. The cubic root of 686561 is about 88.2185082927.

The spelling of 686561 in words is "six hundred eighty-six thousand, five hundred sixty-one".