643803961 has 4 divisors (see below), whose sum is σ = 677688400. Its totient is φ = 609919524.

The previous prime is 643803917. The next prime is 643803967. The reversal of 643803961 is 169308346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 643803961 - 2¹¹ = 643801913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643803967) 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, 16942191 + ... + 16942228.

It is an arithmetic number, because the mean of its divisors is an integer number (169422100).

Almost surely, 2^643803961 is an apocalyptic number.

It is an amenable number.

643803961 is a deficient number, since it is larger than the sum of its proper divisors (33884439).

643803961 is a wasteful number, since it uses less digits than its factorization.

643803961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33884438.

The product of its (nonzero) digits is 93312, while the sum is 40.

The square root of 643803961 is about 25373.2922775110. The cubic root of 643803961 is about 863.4778764295.

The spelling of 643803961 in words is "six hundred forty-three million, eight hundred three thousand, nine hundred sixty-one".