1664209 has 4 divisors (see below), whose sum is σ = 1666980. Its totient is φ = 1661440.

The previous prime is 1664123. The next prime is 1664227. The reversal of 1664209 is 9024661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 9024661 = 229 ⋅39409.

It can be written as a sum of positive squares in 2 ways, for example, as 529984 + 1134225 = 728^2 + 1065^2 .

It is a cyclic number.

It is not a de Polignac number, because 1664209 - 2¹¹ = 1662161 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1664279) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64 + ... + 1825.

It is an arithmetic number, because the mean of its divisors is an integer number (416745).

2^1664209 is an apocalyptic number.

It is an amenable number.

1664209 is a deficient number, since it is larger than the sum of its proper divisors (2771).

1664209 is an equidigital number, since it uses as much as digits as its factorization.

1664209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2770.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 1664209 is about 1290.0422473702. The cubic root of 1664209 is about 118.5048037600.

The spelling of 1664209 in words is "one million, six hundred sixty-four thousand, two hundred nine".