643963891 has 4 divisors (see below), whose sum is σ = 650602792. Its totient is φ = 637324992.

The previous prime is 643963877. The next prime is 643963909. The reversal of 643963891 is 198369346.

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

It is a cyclic number.

It is not a de Polignac number, because 643963891 - 2⁹ = 643963379 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643963871) 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, 3319305 + ... + 3319498.

It is an arithmetic number, because the mean of its divisors is an integer number (162650698).

Almost surely, 2^643963891 is an apocalyptic number.

643963891 is a deficient number, since it is larger than the sum of its proper divisors (6638901).

643963891 is an equidigital number, since it uses as much as digits as its factorization.

643963891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6638900.

The product of its digits is 839808, while the sum is 49.

The square root of 643963891 is about 25376.4436239596. The cubic root of 643963891 is about 863.5493705446.

The spelling of 643963891 in words is "six hundred forty-three million, nine hundred sixty-three thousand, eight hundred ninety-one".