666409 has 4 divisors (see below), whose sum is σ = 668304. Its totient is φ = 664516.

The previous prime is 666403. The next prime is 666427. The reversal of 666409 is 904666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 666409 - 2⁹ = 665897 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666403) 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, 247 + ... + 1180.

It is an arithmetic number, because the mean of its divisors is an integer number (167076).

2⁶⁶⁶⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

666409 is a deficient number, since it is larger than the sum of its proper divisors (1895).

666409 is a wasteful number, since it uses less digits than its factorization.

666409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1894.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 666409 is about 816.3387777143. The cubic root of 666409 is about 87.3467903950.

The spelling of 666409 in words is "six hundred sixty-six thousand, four hundred nine".