666738665 has 4 divisors (see below), whose sum is σ = 800086404. Its totient is φ = 533390928.

The previous prime is 666738647. The next prime is 666738719. The reversal of 666738665 is 566837666.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 362026729 + 304711936 = 19027^2 + 17456^2 .

It is a cyclic number.

It is not a de Polignac number, because 666738665 - 2¹⁴ = 666722281 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66673862 + ... + 66673871.

It is an arithmetic number, because the mean of its divisors is an integer number (200021601).

Almost surely, 2^666738665 is an apocalyptic number.

It is an amenable number.

666738665 is a deficient number, since it is larger than the sum of its proper divisors (133347739).

666738665 is a wasteful number, since it uses less digits than its factorization.

666738665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 133347738.

The product of its digits is 6531840, while the sum is 53.

The square root of 666738665 is about 25821.2831788043. The cubic root of 666738665 is about 873.6119117730.

Subtracting from 666738665 its reverse (566837666), we obtain a palindrome (99900999).

The spelling of 666738665 in words is "six hundred sixty-six million, seven hundred thirty-eight thousand, six hundred sixty-five".