644747839 has 2 divisors, whose sum is σ = 644747840. Its totient is φ = 644747838.

The previous prime is 644747821. The next prime is 644747849. The reversal of 644747839 is 938747446.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 644747839 - 2¹⁷ = 644616767 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644747819) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322373919 + 322373920.

It is an arithmetic number, because the mean of its divisors is an integer number (322373920).

Almost surely, 2^644747839 is an apocalyptic number.

644747839 is a deficient number, since it is larger than the sum of its proper divisors (1).

644747839 is an equidigital number, since it uses as much as digits as its factorization.

644747839 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4064256, while the sum is 52.

The square root of 644747839 is about 25391.8852982602. The cubic root of 644747839 is about 863.8996506789.

The spelling of 644747839 in words is "six hundred forty-four million, seven hundred forty-seven thousand, eight hundred thirty-nine".