644747819 has 2 divisors, whose sum is σ = 644747820. Its totient is φ = 644747818.

The previous prime is 644747801. The next prime is 644747821. The reversal of 644747819 is 918747446.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644747819 is a prime.

It is a super-2 number, since 2×644747819² = 831399500210513522, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 644747821, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644747839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322373909 + 322373910.

It is an arithmetic number, because the mean of its divisors is an integer number (322373910).

Almost surely, 2^644747819 is an apocalyptic number.

644747819 is a deficient number, since it is larger than the sum of its proper divisors (1).

644747819 is an equidigital number, since it uses as much as digits as its factorization.

644747819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1354752, while the sum is 50.

The square root of 644747819 is about 25391.8849044335. The cubic root of 644747819 is about 863.8996417462.

The spelling of 644747819 in words is "six hundred forty-four million, seven hundred forty-seven thousand, eight hundred nineteen".