644636328 has 128 divisors (see below), whose sum is σ = 1966187520. Its totient is φ = 171924480.

The previous prime is 644636327. The next prime is 644636329. The reversal of 644636328 is 823636446.

It is a happy number.

644636328 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (644636327) and next prime (644636329).

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 644636328.

It is not an unprimeable number, because it can be changed into a prime (644636327) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 373275 + ... + 374997.

It is an arithmetic number, because the mean of its divisors is an integer number (15360840).

Almost surely, 2^644636328 is an apocalyptic number.

644636328 is a gapful number since it is divisible by the number (68) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644636328, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (983093760).

644636328 is an abundant number, since it is smaller than the sum of its proper divisors (1321551192).

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

644636328 is a wasteful number, since it uses less digits than its factorization.

644636328 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1887 (or 1883 counting only the distinct ones).

The product of its digits is 497664, while the sum is 42.

The square root of 644636328 is about 25389.6894033779. The cubic root of 644636328 is about 863.8498431612.

The spelling of 644636328 in words is "six hundred forty-four million, six hundred thirty-six thousand, three hundred twenty-eight".