643521557 has 6 divisors (see below), whose sum is σ = 748586358. Its totient is φ = 551589864.

The previous prime is 643521551. The next prime is 643521559. The reversal of 643521557 is 755125346.

It is a happy number.

643521557 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 634334596 + 9186961 = 25186^2 + 3031^2 .

It is not a de Polignac number, because 643521557 - 2¹² = 643517461 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 643521557.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643521551) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6566498 + ... + 6566595.

It is an arithmetic number, because the mean of its divisors is an integer number (124764393).

Almost surely, 2^643521557 is an apocalyptic number.

It is an amenable number.

643521557 is a deficient number, since it is larger than the sum of its proper divisors (105064801).

643521557 is a wasteful number, since it uses less digits than its factorization.

643521557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13133107 (or 13133100 counting only the distinct ones).

The product of its digits is 126000, while the sum is 38.

The square root of 643521557 is about 25367.7266817506. The cubic root of 643521557 is about 863.3516033793.

The spelling of 643521557 in words is "six hundred forty-three million, five hundred twenty-one thousand, five hundred fifty-seven".