643866849 has 6 divisors (see below), whose sum is σ = 930029906. Its totient is φ = 429244560.

The previous prime is 643866809. The next prime is 643866871. The reversal of 643866849 is 948668346.

It can be written as a sum of positive squares in only one way, i.e., 632170449 + 11696400 = 25143^2 + 3420^2 .

It is not a de Polignac number, because 643866849 - 2¹² = 643862753 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 643866795 and 643866804.

It is not an unprimeable number, because it can be changed into a prime (643866809) 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 5 ways as a sum of consecutive naturals, for example, 35770372 + ... + 35770389.

Almost surely, 2^643866849 is an apocalyptic number.

It is an amenable number.

643866849 is a deficient number, since it is larger than the sum of its proper divisors (286163057).

643866849 is a wasteful number, since it uses less digits than its factorization.

643866849 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71540767 (or 71540764 counting only the distinct ones).

The product of its digits is 5971968, while the sum is 54.

The square root of 643866849 is about 25374.5315030642. The cubic root of 643866849 is about 863.5059909033.

The spelling of 643866849 in words is "six hundred forty-three million, eight hundred sixty-six thousand, eight hundred forty-nine".