685508821 has 2 divisors, whose sum is σ = 685508822. Its totient is φ = 685508820.

The previous prime is 685508819. The next prime is 685508839. The reversal of 685508821 is 128805586.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 502880625 + 182628196 = 22425^2 + 13514^2 .

It is a cyclic number.

It is not a de Polignac number, because 685508821 - 2¹ = 685508819 is a prime.

Together with 685508819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (685508801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342754410 + 342754411.

It is an arithmetic number, because the mean of its divisors is an integer number (342754411).

Almost surely, 2^685508821 is an apocalyptic number.

It is an amenable number.

685508821 is a deficient number, since it is larger than the sum of its proper divisors (1).

685508821 is an equidigital number, since it uses as much as digits as its factorization.

685508821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 153600, while the sum is 43.

The square root of 685508821 is about 26182.2233777042. The cubic root of 685508821 is about 881.7341925730.

The spelling of 685508821 in words is "six hundred eighty-five million, five hundred eight thousand, eight hundred twenty-one".