644815813 has 2 divisors, whose sum is σ = 644815814. Its totient is φ = 644815812.

The previous prime is 644815793. The next prime is 644815849. The reversal of 644815813 is 318518446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 633377889 + 11437924 = 25167^2 + 3382^2 .

It is a cyclic number.

It is not a de Polignac number, because 644815813 - 2⁵ = 644815781 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644815883) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322407906 + 322407907.

It is an arithmetic number, because the mean of its divisors is an integer number (322407907).

Almost surely, 2^644815813 is an apocalyptic number.

It is an amenable number.

644815813 is a deficient number, since it is larger than the sum of its proper divisors (1).

644815813 is an equidigital number, since it uses as much as digits as its factorization.

644815813 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 92160, while the sum is 40.

The square root of 644815813 is about 25393.2237614683. The cubic root of 644815813 is about 863.9300091373.

The spelling of 644815813 in words is "six hundred forty-four million, eight hundred fifteen thousand, eight hundred thirteen".