668191217 has 2 divisors, whose sum is σ = 668191218. Its totient is φ = 668191216.

The previous prime is 668191207. The next prime is 668191219. The reversal of 668191217 is 712191866.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 534349456 + 133841761 = 23116^2 + 11569^2 .

It is a cyclic number.

It is not a de Polignac number, because 668191217 - 2⁸ = 668190961 is a prime.

Together with 668191219, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (668191219) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334095608 + 334095609.

It is an arithmetic number, because the mean of its divisors is an integer number (334095609).

Almost surely, 2^668191217 is an apocalyptic number.

It is an amenable number.

668191217 is a deficient number, since it is larger than the sum of its proper divisors (1).

668191217 is an equidigital number, since it uses as much as digits as its factorization.

668191217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 41.

The square root of 668191217 is about 25849.3949058774. The cubic root of 668191217 is about 874.2458664689.

The spelling of 668191217 in words is "six hundred sixty-eight million, one hundred ninety-one thousand, two hundred seventeen".