643626721 has 4 divisors (see below), whose sum is σ = 649642032. Its totient is φ = 637611412.

The previous prime is 643626689. The next prime is 643626773. The reversal of 643626721 is 127626346.

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 643626721 - 2⁵ = 643626689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643626821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3007495 + ... + 3007708.

It is an arithmetic number, because the mean of its divisors is an integer number (162410508).

Almost surely, 2^643626721 is an apocalyptic number.

It is an amenable number.

643626721 is a deficient number, since it is larger than the sum of its proper divisors (6015311).

643626721 is a wasteful number, since it uses less digits than its factorization.

643626721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6015310.

The product of its digits is 72576, while the sum is 37.

The square root of 643626721 is about 25369.7993882490. The cubic root of 643626721 is about 863.3986303264.

The spelling of 643626721 in words is "six hundred forty-three million, six hundred twenty-six thousand, seven hundred twenty-one".