666819665 has 8 divisors (see below), whose sum is σ = 801484200. Its totient is φ = 532588672.

The previous prime is 666819623. The next prime is 666819701. The reversal of 666819665 is 566918666.

It can be written as a sum of positive squares in 4 ways, for example, as 26122321 + 640697344 = 5111^2 + 25312^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 666819665 - 2¹⁰ = 666818641 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 104990 + ... + 111159.

It is an arithmetic number, because the mean of its divisors is an integer number (100185525).

Almost surely, 2^666819665 is an apocalyptic number.

It is an amenable number.

666819665 is a deficient number, since it is larger than the sum of its proper divisors (134664535).

666819665 is a wasteful number, since it uses less digits than its factorization.

666819665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216771.

The product of its digits is 2799360, while the sum is 53.

The square root of 666819665 is about 25822.8516047318. The cubic root of 666819665 is about 873.6472878022.

Subtracting from 666819665 its reverse (566918666), we obtain a palindrome (99900999).

The spelling of 666819665 in words is "six hundred sixty-six million, eight hundred nineteen thousand, six hundred sixty-five".