643871809 has 24 divisors (see below), whose sum is σ = 778021728. Its totient is φ = 530893440.

The previous prime is 643871803. The next prime is 643871873. The reversal of 643871809 is 908178346.

It is a happy number.

It is not a de Polignac number, because 643871809 - 2⁵ = 643871777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643871803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 138889 + ... + 143449.

It is an arithmetic number, because the mean of its divisors is an integer number (32417572).

Almost surely, 2^643871809 is an apocalyptic number.

It is an amenable number.

643871809 is a deficient number, since it is larger than the sum of its proper divisors (134149919).

643871809 is a wasteful number, since it uses less digits than its factorization.

643871809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4685 (or 4678 counting only the distinct ones).

The product of its (nonzero) digits is 290304, while the sum is 46.

The square root of 643871809 is about 25374.6292386707. The cubic root of 643871809 is about 863.5082082244.

It can be divided in two parts, 643871 and 809, that added together give a triangular number (644680 = T₁₁₃₅).

The spelling of 643871809 in words is "six hundred forty-three million, eight hundred seventy-one thousand, eight hundred nine".