644936819 has 2 divisors, whose sum is σ = 644936820. Its totient is φ = 644936818.

The previous prime is 644936797. The next prime is 644936839. The reversal of 644936819 is 918639446.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644936819 is a prime.

It is a super-2 number, since 2×644936819² = 831887001003677522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644936839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322468409 + 322468410.

It is an arithmetic number, because the mean of its divisors is an integer number (322468410).

Almost surely, 2^644936819 is an apocalyptic number.

644936819 is a deficient number, since it is larger than the sum of its proper divisors (1).

644936819 is an equidigital number, since it uses as much as digits as its factorization.

644936819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1119744, while the sum is 50.

The square root of 644936819 is about 25395.6062932154. The cubic root of 644936819 is about 863.9840473985.

The spelling of 644936819 in words is "six hundred forty-four million, nine hundred thirty-six thousand, eight hundred nineteen".