643918765 has 32 divisors (see below), whose sum is σ = 916160256. Its totient is φ = 425295360.

The previous prime is 643918757. The next prime is 643918771. The reversal of 643918765 is 567819346.

It is not a de Polignac number, because 643918765 - 2³ = 643918757 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 106935 + ... + 112795.

It is an arithmetic number, because the mean of its divisors is an integer number (28630008).

Almost surely, 2^643918765 is an apocalyptic number.

It is an amenable number.

643918765 is a deficient number, since it is larger than the sum of its proper divisors (272241491).

643918765 is a wasteful number, since it uses less digits than its factorization.

643918765 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5989.

The product of its digits is 1088640, while the sum is 49.

The square root of 643918765 is about 25375.5544767006. The cubic root of 643918765 is about 863.5291988964.

The spelling of 643918765 in words is "six hundred forty-three million, nine hundred eighteen thousand, seven hundred sixty-five".