664240921 has 2 divisors, whose sum is σ = 664240922. Its totient is φ = 664240920.

The previous prime is 664240919. The next prime is 664240979. The reversal of 664240921 is 129042466.

664240921 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., 496175625 + 168065296 = 22275^2 + 12964^2 .

It is a cyclic number.

It is not a de Polignac number, because 664240921 - 2¹ = 664240919 is a prime.

It is a super-5 number, since 5×664240921⁵ (a number of 45 digits) contains 55555 as substring. Note that it is a super-d number also for d = 2.

Together with 664240919, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (664240901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332120460 + 332120461.

It is an arithmetic number, because the mean of its divisors is an integer number (332120461).

Almost surely, 2^664240921 is an apocalyptic number.

It is an amenable number.

664240921 is a deficient number, since it is larger than the sum of its proper divisors (1).

664240921 is an equidigital number, since it uses as much as digits as its factorization.

664240921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20736, while the sum is 34.

The square root of 664240921 is about 25772.8718035069. The cubic root of 664240921 is about 872.5196350291.

The spelling of 664240921 in words is "six hundred sixty-four million, two hundred forty thousand, nine hundred twenty-one".