644663 has 4 divisors (see below), whose sum is σ = 653568. Its totient is φ = 635760.

The previous prime is 644653. The next prime is 644669. The reversal of 644663 is 366446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 644663 - 2⁴ = 644647 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644669) 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, 4343 + ... + 4488.

It is an arithmetic number, because the mean of its divisors is an integer number (163392).

2⁶⁴⁴⁶⁶³ is an apocalyptic number.

644663 is a deficient number, since it is larger than the sum of its proper divisors (8905).

644663 is an equidigital number, since it uses as much as digits as its factorization.

644663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8904.

The product of its digits is 10368, while the sum is 29.

The square root of 644663 is about 802.9090857625. The cubic root of 644663 is about 86.3861757003.

The spelling of 644663 in words is "six hundred forty-four thousand, six hundred sixty-three".