644710621 has 2 divisors, whose sum is σ = 644710622. Its totient is φ = 644710620.

The previous prime is 644710613. The next prime is 644710637. The reversal of 644710621 is 126017446.

644710621 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., 622752025 + 21958596 = 24955^2 + 4686^2 .

It is a cyclic number.

It is not a de Polignac number, because 644710621 - 2³ = 644710613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644710721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322355310 + 322355311.

It is an arithmetic number, because the mean of its divisors is an integer number (322355311).

Almost surely, 2^644710621 is an apocalyptic number.

It is an amenable number.

644710621 is a deficient number, since it is larger than the sum of its proper divisors (1).

644710621 is an equidigital number, since it uses as much as digits as its factorization.

644710621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8064, while the sum is 31.

The square root of 644710621 is about 25391.1524157530. The cubic root of 644710621 is about 863.8830275208.

The spelling of 644710621 in words is "six hundred forty-four million, seven hundred ten thousand, six hundred twenty-one".