685709561 has 2 divisors, whose sum is σ = 685709562. Its totient is φ = 685709560.

The previous prime is 685709539. The next prime is 685709579. The reversal of 685709561 is 165907586.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 656333161 + 29376400 = 25619^2 + 5420^2 .

It is a cyclic number.

It is not a de Polignac number, because 685709561 - 2²² = 681515257 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (685702561) 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 as a sum of consecutive naturals, namely, 342854780 + 342854781.

It is an arithmetic number, because the mean of its divisors is an integer number (342854781).

Almost surely, 2^685709561 is an apocalyptic number.

It is an amenable number.

685709561 is a deficient number, since it is larger than the sum of its proper divisors (1).

685709561 is an equidigital number, since it uses as much as digits as its factorization.

685709561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 453600, while the sum is 47.

The square root of 685709561 is about 26186.0566141601. The cubic root of 685709561 is about 881.8202512990.

The spelling of 685709561 in words is "six hundred eighty-five million, seven hundred nine thousand, five hundred sixty-one".