643764881 has 16 divisors (see below), whose sum is σ = 684754560. Its totient is φ = 604275840.

The previous prime is 643764851. The next prime is 643764883. The reversal of 643764881 is 188467346.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 643764881 - 2²² = 639570577 is a prime.

It is a super-2 number, since 2×643764881² = 828866444017888322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643764883) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 148166 + ... + 152448.

It is an arithmetic number, because the mean of its divisors is an integer number (42797160).

Almost surely, 2^643764881 is an apocalyptic number.

It is an amenable number.

643764881 is a deficient number, since it is larger than the sum of its proper divisors (40989679).

643764881 is a wasteful number, since it uses less digits than its factorization.

643764881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4456.

The product of its digits is 774144, while the sum is 47.

The square root of 643764881 is about 25372.5221647356. The cubic root of 643764881 is about 863.4604045487.

The spelling of 643764881 in words is "six hundred forty-three million, seven hundred sixty-four thousand, eight hundred eighty-one".