644564621 has 2 divisors, whose sum is σ = 644564622. Its totient is φ = 644564620.

The previous prime is 644564579. The next prime is 644564623. The reversal of 644564621 is 126465446.

644564621 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 can be written as a sum of positive squares in only one way, i.e., 478515625 + 166048996 = 21875^2 + 12886^2 .

It is a cyclic number.

It is not a de Polignac number, because 644564621 - 2¹⁴ = 644548237 is a prime.

It is a Sophie Germain prime.

Together with 644564623, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644564623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322282310 + 322282311.

It is an arithmetic number, because the mean of its divisors is an integer number (322282311).

Almost surely, 2^644564621 is an apocalyptic number.

It is an amenable number.

644564621 is a deficient number, since it is larger than the sum of its proper divisors (1).

644564621 is an equidigital number, since it uses as much as digits as its factorization.

644564621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 138240, while the sum is 38.

The square root of 644564621 is about 25388.2772357638. The cubic root of 644564621 is about 863.8178114688.

The spelling of 644564621 in words is "six hundred forty-four million, five hundred sixty-four thousand, six hundred twenty-one".