664687021 has 2 divisors, whose sum is σ = 664687022. Its totient is φ = 664687020.

The previous prime is 664687007. The next prime is 664687033. The reversal of 664687021 is 120786466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 658486921 + 6200100 = 25661^2 + 2490^2 .

It is a cyclic number.

It is not a de Polignac number, because 664687021 - 2⁹ = 664686509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664687061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332343510 + 332343511.

It is an arithmetic number, because the mean of its divisors is an integer number (332343511).

Almost surely, 2^664687021 is an apocalyptic number.

It is an amenable number.

664687021 is a deficient number, since it is larger than the sum of its proper divisors (1).

664687021 is an equidigital number, since it uses as much as digits as its factorization.

664687021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 96768, while the sum is 40.

The square root of 664687021 is about 25781.5247997476. The cubic root of 664687021 is about 872.7149175410.

The spelling of 664687021 in words is "six hundred sixty-four million, six hundred eighty-seven thousand, twenty-one".