643564673 has 4 divisors (see below), whose sum is σ = 643910148. Its totient is φ = 643219200.

The previous prime is 643564657. The next prime is 643564687. The reversal of 643564673 is 376465346.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 376465346 = 2 ⋅188232673.

It can be written as a sum of positive squares in 2 ways, for example, as 158331889 + 485232784 = 12583^2 + 22028^2 .

It is a cyclic number.

It is not a de Polignac number, because 643564673 - 2⁴ = 643564657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643564613) 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, 169928 + ... + 173673.

It is an arithmetic number, because the mean of its divisors is an integer number (160977537).

Almost surely, 2^643564673 is an apocalyptic number.

It is an amenable number.

643564673 is a deficient number, since it is larger than the sum of its proper divisors (345475).

643564673 is a wasteful number, since it uses less digits than its factorization.

643564673 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 345474.

The product of its digits is 1088640, while the sum is 44.

The square root of 643564673 is about 25368.5764874579. The cubic root of 643564673 is about 863.3708844927.

The spelling of 643564673 in words is "six hundred forty-three million, five hundred sixty-four thousand, six hundred seventy-three".