668491931 has 2 divisors, whose sum is σ = 668491932. Its totient is φ = 668491930.

The previous prime is 668491919. The next prime is 668491937. The reversal of 668491931 is 139194866.

668491931 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-668491931 is a prime.

It is a super-2 number, since 2×668491931² = 893762923624217522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (668491937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334245965 + 334245966.

It is an arithmetic number, because the mean of its divisors is an integer number (334245966).

Almost surely, 2^668491931 is an apocalyptic number.

668491931 is a deficient number, since it is larger than the sum of its proper divisors (1).

668491931 is an equidigital number, since it uses as much as digits as its factorization.

668491931 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 279936, while the sum is 47.

The square root of 668491931 is about 25855.2109061210. The cubic root of 668491931 is about 874.3769958703.

The spelling of 668491931 in words is "six hundred sixty-eight million, four hundred ninety-one thousand, nine hundred thirty-one".