643943221 has 4 divisors (see below), whose sum is σ = 681822252. Its totient is φ = 606064192.

The previous prime is 643943219. The next prime is 643943239. The reversal of 643943221 is 122349346.

It is a happy number.

643943221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 185340996 + 458602225 = 13614^2 + 21415^2 .

It is a cyclic number.

It is not a de Polignac number, because 643943221 - 2¹ = 643943219 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643943291) 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, 18939490 + ... + 18939523.

It is an arithmetic number, because the mean of its divisors is an integer number (170455563).

Almost surely, 2^643943221 is an apocalyptic number.

It is an amenable number.

643943221 is a deficient number, since it is larger than the sum of its proper divisors (37879031).

643943221 is a wasteful number, since it uses less digits than its factorization.

643943221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37879030.

The product of its digits is 31104, while the sum is 34.

The square root of 643943221 is about 25376.0363532211. The cubic root of 643943221 is about 863.5401310221.

The spelling of 643943221 in words is "six hundred forty-three million, nine hundred forty-three thousand, two hundred twenty-one".