643485721 has 4 divisors (see below), whose sum is σ = 645682212. Its totient is φ = 641289232.

The previous prime is 643485719. The next prime is 643485737. The reversal of 643485721 is 127584346.

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

It can be written as a sum of positive squares in 2 ways, for example, as 566678025 + 76807696 = 23805^2 + 8764^2 .

It is a cyclic number.

It is not a de Polignac number, because 643485721 - 2¹ = 643485719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643485701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1097806 + ... + 1098391.

It is an arithmetic number, because the mean of its divisors is an integer number (161420553).

Almost surely, 2^643485721 is an apocalyptic number.

It is an amenable number.

643485721 is a deficient number, since it is larger than the sum of its proper divisors (2196491).

643485721 is a wasteful number, since it uses less digits than its factorization.

643485721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2196490.

The product of its digits is 161280, while the sum is 40.

The square root of 643485721 is about 25367.0203413803. The cubic root of 643485721 is about 863.3355771654.

The spelling of 643485721 in words is "six hundred forty-three million, four hundred eighty-five thousand, seven hundred twenty-one".