643784521 has 4 divisors (see below), whose sum is σ = 657482112. Its totient is φ = 630086932.

The previous prime is 643784507. The next prime is 643784527. The reversal of 643784521 is 125487346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 643784521 - 2¹¹ = 643782473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643784527) 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, 6848725 + ... + 6848818.

It is an arithmetic number, because the mean of its divisors is an integer number (164370528).

Almost surely, 2^643784521 is an apocalyptic number.

It is an amenable number.

643784521 is a deficient number, since it is larger than the sum of its proper divisors (13697591).

643784521 is a wasteful number, since it uses less digits than its factorization.

643784521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13697590.

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

The square root of 643784521 is about 25372.9091946509. The cubic root of 643784521 is about 863.4691852855.

The spelling of 643784521 in words is "six hundred forty-three million, seven hundred eighty-four thousand, five hundred twenty-one".