1685821 has 2 divisors, whose sum is σ = 1685822. Its totient is φ = 1685820.

The previous prime is 1685819. The next prime is 1685833. The reversal of 1685821 is 1285861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1651225 + 34596 = 1285^2 + 186^2 .

It is a cyclic number.

It is not a de Polignac number, because 1685821 - 2¹ = 1685819 is a prime.

Together with 1685819, 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 (1685861) 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, 842910 + 842911.

It is an arithmetic number, because the mean of its divisors is an integer number (842911).

2^1685821 is an apocalyptic number.

It is an amenable number.

1685821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1685821 is an equidigital number, since it uses as much as digits as its factorization.

1685821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3840, while the sum is 31.

The square root of 1685821 is about 1298.3916974473. The cubic root of 1685821 is about 119.0155806636.

The spelling of 1685821 in words is "one million, six hundred eighty-five thousand, eight hundred twenty-one".