644005621 has 4 divisors (see below), whose sum is σ = 736006432. Its totient is φ = 552004812.

The previous prime is 644005619. The next prime is 644005631. The reversal of 644005621 is 126500446.

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 644005621 - 2¹ = 644005619 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644005621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644005631) 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, 46000395 + ... + 46000408.

It is an arithmetic number, because the mean of its divisors is an integer number (184001608).

Almost surely, 2^644005621 is an apocalyptic number.

It is an amenable number.

644005621 is a deficient number, since it is larger than the sum of its proper divisors (92000811).

644005621 is an equidigital number, since it uses as much as digits as its factorization.

644005621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92000810.

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 644005621 is about 25377.2658298722. The cubic root of 644005621 is about 863.5680233176.

The spelling of 644005621 in words is "six hundred forty-four million, five thousand, six hundred twenty-one".