666666665 has 32 divisors (see below), whose sum is σ = 938338560. Its totient is φ = 445261824.

The previous prime is 666666653. The next prime is 666666667. The reversal of 666666665 is 566666666.

It is a happy number.

It is not a de Polignac number, because 666666665 - 2¹⁶ = 666601129 is a prime.

It is a Smith number, since the sum of its digits (53) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (666666667) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 231917 + ... + 234773.

It is an arithmetic number, because the mean of its divisors is an integer number (29323080).

Almost surely, 2^666666665 is an apocalyptic number.

It is an amenable number.

666666665 is a deficient number, since it is larger than the sum of its proper divisors (271671895).

666666665 is a wasteful number, since it uses less digits than its factorization.

666666665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3041.

The product of its digits is 8398080, while the sum is 53.

The square root of 666666665 is about 25819.8889424413. Note that the first 3 decimals coincide. The cubic root of 666666665 is about 873.5804640083.

Subtracting from 666666665 its reverse (566666666), we obtain a palindrome (99999999).

The spelling of 666666665 in words is "six hundred sixty-six million, six hundred sixty-six thousand, six hundred sixty-five".