685609 has 2 divisors, whose sum is σ = 685610. Its totient is φ = 685608.

The previous prime is 685591. The next prime is 685613. The reversal of 685609 is 906586.

685609 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 685584 + 25 = 828^2 + 5^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-685609 is a prime.

It is an Ulam number.

685609 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (685649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342804 + 342805.

It is an arithmetic number, because the mean of its divisors is an integer number (342805).

2⁶⁸⁵⁶⁰⁹ is an apocalyptic number.

It is an amenable number.

685609 is a deficient number, since it is larger than the sum of its proper divisors (1).

685609 is an equidigital number, since it uses as much as digits as its factorization.

685609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 685609 is about 828.0150964807. The cubic root of 685609 is about 88.1777142153.

The spelling of 685609 in words is "six hundred eighty-five thousand, six hundred nine".