643844881 has 8 divisors (see below), whose sum is σ = 663828840. Its totient is φ = 623996928.

The previous prime is 643844843. The next prime is 643844899. The reversal of 643844881 is 188448346.

It can be written as a sum of positive squares in 4 ways, for example, as 224250625 + 419594256 = 14975^2 + 20484^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 643844881 - 2⁷ = 643844753 is a prime.

It is a super-2 number, since 2×643844881² = 829072461579808322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (643844381) 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 7 ways as a sum of consecutive naturals, for example, 24346 + ... + 43363.

It is an arithmetic number, because the mean of its divisors is an integer number (82978605).

Almost surely, 2^643844881 is an apocalyptic number.

It is an amenable number.

643844881 is a deficient number, since it is larger than the sum of its proper divisors (19983959).

643844881 is a wasteful number, since it uses less digits than its factorization.

643844881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68003.

The product of its digits is 589824, while the sum is 46.

The square root of 643844881 is about 25374.0986243847. The cubic root of 643844881 is about 863.4961701795.

The spelling of 643844881 in words is "six hundred forty-three million, eight hundred forty-four thousand, eight hundred eighty-one".