666909665 has 16 divisors (see below), whose sum is σ = 854599680. Its totient is φ = 498509760.

The previous prime is 666909641. The next prime is 666909673. The reversal of 666909665 is 566909666.

It is a happy number.

666909665 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 666909665 - 2⁸ = 666909409 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 69689 + ... + 78678.

It is an arithmetic number, because the mean of its divisors is an integer number (53412480).

Almost surely, 2^666909665 is an apocalyptic number.

It is an amenable number.

666909665 is a deficient number, since it is larger than the sum of its proper divisors (187690015).

666909665 is a wasteful number, since it uses less digits than its factorization.

666909665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148432.

The product of its (nonzero) digits is 3149280, while the sum is 53.

The square root of 666909665 is about 25824.5941884863. The cubic root of 666909665 is about 873.6865911416.

Subtracting from 666909665 its reverse (566909666), we obtain a palindrome (99999999).

The spelling of 666909665 in words is "six hundred sixty-six million, nine hundred nine thousand, six hundred sixty-five".