666665 has 8 divisors (see below), whose sum is σ = 806208. Its totient is φ = 529200.

The previous prime is 666649. The next prime is 666667. The reversal of 666665 is 566666.

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

It is not a de Polignac number, because 666665 - 2⁴ = 666649 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 10.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 666665.

It is not an unprimeable number, because it can be changed into a prime (666667) 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, 314 + ... + 1196.

It is an arithmetic number, because the mean of its divisors is an integer number (100776).

2⁶⁶⁶⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

666665 is a deficient number, since it is larger than the sum of its proper divisors (139543).

666665 is a wasteful number, since it uses less digits than its factorization.

666665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1039.

The product of its digits is 38880, while the sum is 35.

The square root of 666665 is about 816.4955603064. The cubic root of 666665 is about 87.3579736752.

Subtracting from 666665 its reverse (566666), we obtain a palindrome (99999).

It can be divided in two parts, 666 and 665, that added together give a palindrome (1331).

The spelling of 666665 in words is "six hundred sixty-six thousand, six hundred sixty-five".