666856717 has 4 divisors (see below), whose sum is σ = 688368256. Its totient is φ = 645345180.

The previous prime is 666856703. The next prime is 666856741. The reversal of 666856717 is 717658666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 717658666 = 2 ⋅358829333.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666856717 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666854717) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10755723 + ... + 10755784.

It is an arithmetic number, because the mean of its divisors is an integer number (172092064).

Almost surely, 2^666856717 is an apocalyptic number.

It is an amenable number.

666856717 is a deficient number, since it is larger than the sum of its proper divisors (21511539).

666856717 is a wasteful number, since it uses less digits than its factorization.

666856717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21511538.

The product of its digits is 2540160, while the sum is 52.

The square root of 666856717 is about 25823.5690213417. The cubic root of 666856717 is about 873.6634689786.

The spelling of 666856717 in words is "six hundred sixty-six million, eight hundred fifty-six thousand, seven hundred seventeen".