643876985 has 4 divisors (see below), whose sum is σ = 772652388. Its totient is φ = 515101584.

The previous prime is 643876963. The next prime is 643877011. The reversal of 643876985 is 589678346.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 589678346 = 2 ⋅294839173.

It can be written as a sum of positive squares in 2 ways, for example, as 505485289 + 138391696 = 22483^2 + 11764^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643876985 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 643876985.

It is an unprimeable number.

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, 64387694 + ... + 64387703.

It is an arithmetic number, because the mean of its divisors is an integer number (193163097).

Almost surely, 2^643876985 is an apocalyptic number.

It is an amenable number.

643876985 is a deficient number, since it is larger than the sum of its proper divisors (128775403).

643876985 is a wasteful number, since it uses less digits than its factorization.

643876985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128775402.

The product of its digits is 8709120, while the sum is 56.

The square root of 643876985 is about 25374.7312301037. The cubic root of 643876985 is about 863.5105220941.

The spelling of 643876985 in words is "six hundred forty-three million, eight hundred seventy-six thousand, nine hundred eighty-five".