644343881 has 2 divisors, whose sum is σ = 644343882. Its totient is φ = 644343880.

The previous prime is 644343871. The next prime is 644343893. The reversal of 644343881 is 188343446.

644343881 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 can be written as a sum of positive squares in only one way, i.e., 635846656 + 8497225 = 25216^2 + 2915^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644343881 is a prime.

It is a super-2 number, since 2×644343881² = 830358073964284322, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644343811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322171940 + 322171941.

It is an arithmetic number, because the mean of its divisors is an integer number (322171941).

Almost surely, 2^644343881 is an apocalyptic number.

It is an amenable number.

644343881 is a deficient number, since it is larger than the sum of its proper divisors (1).

644343881 is an equidigital number, since it uses as much as digits as its factorization.

644343881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 221184, while the sum is 41.

The square root of 644343881 is about 25383.9295815285. The cubic root of 644343881 is about 863.7191914554.

The spelling of 644343881 in words is "six hundred forty-four million, three hundred forty-three thousand, eight hundred eighty-one".