665485209 has 9 divisors (see below), whose sum is σ = 961368213. Its totient is φ = 443605212.

The previous prime is 665485187. The next prime is 665485217. The reversal of 665485209 is 902584566.

The square root of 665485209 is 25797.

It is a perfect power (a square), and thus also a powerful number.

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 665485209 - 2⁹ = 665484697 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (665485229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 73092 + ... + 81690.

Almost surely, 2^665485209 is an apocalyptic number.

665485209 is the 25797-th square number.

665485209 is the 12899-th centered octagonal number.

It is an amenable number.

665485209 is a deficient number, since it is larger than the sum of its proper divisors (295883004).

665485209 is an frugal number, since it uses more digits than its factorization.

665485209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17204 (or 8602 counting only the distinct ones).

The product of its (nonzero) digits is 518400, while the sum is 45.

The cubic root of 665485209 is about 873.0641104219.

Multiplying 665485209 by its product of nonzero digits (518400), we get a square (344987532345600 = 18573840²).

The spelling of 665485209 in words is "six hundred sixty-five million, four hundred eighty-five thousand, two hundred nine".