644001663 has 8 divisors (see below), whose sum is σ = 858832128. Its totient is φ = 429252824.

The previous prime is 644001647. The next prime is 644001689. The reversal of 644001663 is 366100446.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644001663 - 2⁴ = 644001647 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644001663.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644001643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1306 + ... + 35912.

It is an arithmetic number, because the mean of its divisors is an integer number (107354016).

Almost surely, 2^644001663 is an apocalyptic number.

644001663 is a deficient number, since it is larger than the sum of its proper divisors (214830465).

644001663 is a wasteful number, since it uses less digits than its factorization.

644001663 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40813.

The product of its (nonzero) digits is 10368, while the sum is 30.

The square root of 644001663 is about 25377.1878465680. The cubic root of 644001663 is about 863.5662541771.

The spelling of 644001663 in words is "six hundred forty-four million, one thousand, six hundred sixty-three".