668644591 has 2 divisors, whose sum is σ = 668644592. Its totient is φ = 668644590.

The previous prime is 668644583. The next prime is 668644601. The reversal of 668644591 is 195446866.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 668644591 - 2³ = 668644583 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 (668644511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334322295 + 334322296.

It is an arithmetic number, because the mean of its divisors is an integer number (334322296).

Almost surely, 2^668644591 is an apocalyptic number.

668644591 is a deficient number, since it is larger than the sum of its proper divisors (1).

668644591 is an equidigital number, since it uses as much as digits as its factorization.

668644591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1244160, while the sum is 49.

The square root of 668644591 is about 25858.1629471237. The cubic root of 668644591 is about 874.4435497689.

The spelling of 668644591 in words is "six hundred sixty-eight million, six hundred forty-four thousand, five hundred ninety-one".