644837891 has 2 divisors, whose sum is σ = 644837892. Its totient is φ = 644837890.

The previous prime is 644837849. The next prime is 644837953. The reversal of 644837891 is 198738446.

644837891 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 644837891 - 2¹⁰ = 644836867 is a prime.

It is not a weakly prime, because it can be changed into another prime (644830891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322418945 + 322418946.

It is an arithmetic number, because the mean of its divisors is an integer number (322418946).

Almost surely, 2^644837891 is an apocalyptic number.

644837891 is a deficient number, since it is larger than the sum of its proper divisors (1).

644837891 is an equidigital number, since it uses as much as digits as its factorization.

644837891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1161216, while the sum is 50.

The square root of 644837891 is about 25393.6584800221. The cubic root of 644837891 is about 863.9398691256.

The spelling of 644837891 in words is "six hundred forty-four million, eight hundred thirty-seven thousand, eight hundred ninety-one".