643531221 has 24 divisors (see below), whose sum is σ = 937591200. Its totient is φ = 425325600.

The previous prime is 643531183. The next prime is 643531223. The reversal of 643531221 is 122135346.

643531221 is a `hidden beast` number, since 6 + 435 + 3 + 1 + 221 = 666.

643531221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 643531221 - 2⁹ = 643530709 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643531223) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 662266 + ... + 663236.

It is an arithmetic number, because the mean of its divisors is an integer number (39066300).

Almost surely, 2^643531221 is an apocalyptic number.

It is an amenable number.

643531221 is a deficient number, since it is larger than the sum of its proper divisors (294059979).

643531221 is a wasteful number, since it uses less digits than its factorization.

643531221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1537 (or 1534 counting only the distinct ones).

The product of its digits is 4320, while the sum is 27.

The square root of 643531221 is about 25367.9171592782. The cubic root of 643531221 is about 863.3559251139.

Adding to 643531221 its reverse (122135346), we get a palindrome (765666567).

The spelling of 643531221 in words is "six hundred forty-three million, five hundred thirty-one thousand, two hundred twenty-one".