664688681 has 2 divisors, whose sum is σ = 664688682. Its totient is φ = 664688680.

The previous prime is 664688669. The next prime is 664688737. The reversal of 664688681 is 186886466.

664688681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 370909081 + 293779600 = 19259^2 + 17140^2 .

It is a cyclic number.

It is not a de Polignac number, because 664688681 - 2¹⁰ = 664687657 is a prime.

It is a super-2 number, since 2×664688681² = 883622085299039522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (664688881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332344340 + 332344341.

It is an arithmetic number, because the mean of its divisors is an integer number (332344341).

Almost surely, 2^664688681 is an apocalyptic number.

It is an amenable number.

664688681 is a deficient number, since it is larger than the sum of its proper divisors (1).

664688681 is an equidigital number, since it uses as much as digits as its factorization.

664688681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2654208, while the sum is 53.

The square root of 664688681 is about 25781.5569933237. The cubic root of 664688681 is about 872.7156440511.

The spelling of 664688681 in words is "six hundred sixty-four million, six hundred eighty-eight thousand, six hundred eighty-one".