640209 has 8 divisors (see below), whose sum is σ = 868320. Its totient is φ = 419456.

The previous prime is 640193. The next prime is 640219. The reversal of 640209 is 902046.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 640209 - 2⁴ = 640193 is a prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640209.

It is not an unprimeable number, because it can be changed into a prime (640219) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1632 + ... + 1985.

It is an arithmetic number, because the mean of its divisors is an integer number (108540).

2⁶⁴⁰²⁰⁹ is an apocalyptic number.

It is an amenable number.

640209 is a deficient number, since it is larger than the sum of its proper divisors (228111).

640209 is a wasteful number, since it uses less digits than its factorization.

640209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3679.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 640209 is about 800.1306143374. The cubic root of 640209 is about 86.1867673480.

The spelling of 640209 in words is "six hundred forty thousand, two hundred nine".