644734669921 has 2 divisors, whose sum is σ = 644734669922. Its totient is φ = 644734669920.

The previous prime is 644734669903. The next prime is 644734669967. The reversal of 644734669921 is 129966437446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 593539272225 + 51195397696 = 770415^2 + 226264^2 .

It is a cyclic number.

It is not a de Polignac number, because 644734669921 - 2⁹ = 644734669409 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644734669921.

It is not a weakly prime, because it can be changed into another prime (644734669421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322367334960 + 322367334961.

It is an arithmetic number, because the mean of its divisors is an integer number (322367334961).

Almost surely, 2^644734669921 is an apocalyptic number.

It is an amenable number.

644734669921 is a deficient number, since it is larger than the sum of its proper divisors (1).

644734669921 is an equidigital number, since it uses as much as digits as its factorization.

644734669921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 47029248, while the sum is 61.

The spelling of 644734669921 in words is "six hundred forty-four billion, seven hundred thirty-four million, six hundred sixty-nine thousand, nine hundred twenty-one".