643406857 has 4 divisors (see below), whose sum is σ = 643839300. Its totient is φ = 642974416.

The previous prime is 643406849. The next prime is 643406867. The reversal of 643406857 is 758604346.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 454371856 + 189035001 = 21316^2 + 13749^2 .

It is a cyclic number.

It is not a de Polignac number, because 643406857 - 2³ = 643406849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643406867) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 213982 + ... + 216967.

It is an arithmetic number, because the mean of its divisors is an integer number (160959825).

Almost surely, 2^643406857 is an apocalyptic number.

It is an amenable number.

643406857 is a deficient number, since it is larger than the sum of its proper divisors (432443).

643406857 is a wasteful number, since it uses less digits than its factorization.

643406857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 432442.

The product of its (nonzero) digits is 483840, while the sum is 43.

The square root of 643406857 is about 25365.4658344766. The cubic root of 643406857 is about 863.3003063083.

The spelling of 643406857 in words is "six hundred forty-three million, four hundred six thousand, eight hundred fifty-seven".