644905638 has 160 divisors (see below), whose sum is σ = 1668522240. Its totient is φ = 184524480.

The previous prime is 644905633. The next prime is 644905649. The reversal of 644905638 is 836509446.

644905638 is a `hidden beast` number, since 6 + 4 + 4 + 9 + 0 + 5 + 638 = 666.

644905638 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a junction number, because it is equal to n+sod(n) for n = 644905593 and 644905602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644905633) by changing a digit.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 2840881 + ... + 2841107.

It is an arithmetic number, because the mean of its divisors is an integer number (10428264).

Almost surely, 2^644905638 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644905638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (834261120).

644905638 is an abundant number, since it is smaller than the sum of its proper divisors (1023616602).

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

644905638 is a wasteful number, since it uses less digits than its factorization.

644905638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 344 (or 335 counting only the distinct ones).

The product of its (nonzero) digits is 622080, while the sum is 45.

The square root of 644905638 is about 25394.9923803887. The cubic root of 644905638 is about 863.9701233882.

The spelling of 644905638 in words is "six hundred forty-four million, nine hundred five thousand, six hundred thirty-eight".