643776985 has 4 divisors (see below), whose sum is σ = 772532388. Its totient is φ = 515021584.

The previous prime is 643776977. The next prime is 643776989. The reversal of 643776985 is 589677346.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 589677346 = 2 ⋅294838673.

It can be written as a sum of positive squares in 2 ways, for example, as 378380304 + 265396681 = 19452^2 + 16291^2 .

It is a cyclic number.

It is not a de Polignac number, because 643776985 - 2³ = 643776977 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643776989) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64377694 + ... + 64377703.

It is an arithmetic number, because the mean of its divisors is an integer number (193133097).

Almost surely, 2^643776985 is an apocalyptic number.

It is an amenable number.

643776985 is a deficient number, since it is larger than the sum of its proper divisors (128755403).

643776985 is a wasteful number, since it uses less digits than its factorization.

643776985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128755402.

The product of its digits is 7620480, while the sum is 55.

The square root of 643776985 is about 25372.7606893692. The cubic root of 643776985 is about 863.4658160789.

The spelling of 643776985 in words is "six hundred forty-three million, seven hundred seventy-six thousand, nine hundred eighty-five".