643643621 has 4 divisors (see below), whose sum is σ = 643946112. Its totient is φ = 643341132.

The previous prime is 643643587. The next prime is 643643641. The reversal of 643643621 is 126346346.

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 a de Polignac number, because none of the positive numbers 2^k-643643621 is a prime.

It is a super-2 number, since 2×643643621² = 828554221707983282, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643643641) 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, 148031 + ... + 152316.

It is an arithmetic number, because the mean of its divisors is an integer number (160986528).

Almost surely, 2^643643621 is an apocalyptic number.

It is an amenable number.

643643621 is a deficient number, since it is larger than the sum of its proper divisors (302491).

643643621 is a wasteful number, since it uses less digits than its factorization.

643643621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 302490.

The product of its digits is 62208, while the sum is 35.

The square root of 643643621 is about 25370.1324592522. The cubic root of 643643621 is about 863.4061871440.

Adding to 643643621 its reverse (126346346), we get a palindrome (769989967).

The spelling of 643643621 in words is "six hundred forty-three million, six hundred forty-three thousand, six hundred twenty-one".