1686409 has 2 divisors, whose sum is σ = 1686410. Its totient is φ = 1686408.

The previous prime is 1686403. The next prime is 1686439. The reversal of 1686409 is 9046861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1108809 + 577600 = 1053^2 + 760^2 .

It is an emirp because it is prime and its reverse (9046861) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1686409 - 2⁹ = 1685897 is a prime.

1686409 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1686403) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 843204 + 843205.

It is an arithmetic number, because the mean of its divisors is an integer number (843205).

2^1686409 is an apocalyptic number.

It is an amenable number.

1686409 is a deficient number, since it is larger than the sum of its proper divisors (1).

1686409 is an equidigital number, since it uses as much as digits as its factorization.

1686409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 1686409 is about 1298.6181116864. The cubic root of 1686409 is about 119.0294162620.

The spelling of 1686409 in words is "one million, six hundred eighty-six thousand, four hundred nine".