668857391 has 2 divisors, whose sum is σ = 668857392. Its totient is φ = 668857390.

The previous prime is 668857381. The next prime is 668857447. The reversal of 668857391 is 193758866.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 668857391 - 2²⁶ = 601748527 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668857381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334428695 + 334428696.

It is an arithmetic number, because the mean of its divisors is an integer number (334428696).

Almost surely, 2^668857391 is an apocalyptic number.

668857391 is a deficient number, since it is larger than the sum of its proper divisors (1).

668857391 is an equidigital number, since it uses as much as digits as its factorization.

668857391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2177280, while the sum is 53.

The square root of 668857391 is about 25862.2773745856. The cubic root of 668857391 is about 874.5363054984.

The spelling of 668857391 in words is "six hundred sixty-eight million, eight hundred fifty-seven thousand, three hundred ninety-one".