644820064 has 96 divisors (see below), whose sum is σ = 1543945536. Its totient is φ = 258785280.

The previous prime is 644820061. The next prime is 644820073. The reversal of 644820064 is 460028446.

It is a happy number.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (34).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644820061) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1191634 + ... + 1192174.

It is an arithmetic number, because the mean of its divisors is an integer number (16082766).

Almost surely, 2^644820064 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644820064, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (771972768).

644820064 is an abundant number, since it is smaller than the sum of its proper divisors (899125472).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644820064 is a wasteful number, since it uses less digits than its factorization.

644820064 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 888 (or 880 counting only the distinct ones).

The product of its (nonzero) digits is 36864, while the sum is 34.

The square root of 644820064 is about 25393.3074647632. The cubic root of 644820064 is about 863.9319076424.

The spelling of 644820064 in words is "six hundred forty-four million, eight hundred twenty thousand, sixty-four".