644188128 has 48 divisors (see below), whose sum is σ = 1698633216. Its totient is φ = 213759360.

The previous prime is 644188099. The next prime is 644188151. The reversal of 644188128 is 821881446.

It is a tau number, because it is divible by the number of its divisors (48).

It is a super-2 number, since 2×644188128² = 829956688512288768, which contains 22 as substring.

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 644188128.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6363 + ... + 36453.

It is an arithmetic number, because the mean of its divisors is an integer number (35388192).

Almost surely, 2^644188128 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 644188128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (849316608).

644188128 is an abundant number, since it is smaller than the sum of its proper divisors (1054445088).

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

644188128 is a wasteful number, since it uses less digits than its factorization.

644188128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30327 (or 30319 counting only the distinct ones).

The product of its digits is 98304, while the sum is 42.

The square root of 644188128 is about 25380.8614511013. The cubic root of 644188128 is about 863.6495921311.

The spelling of 644188128 in words is "six hundred forty-four million, one hundred eighty-eight thousand, one hundred twenty-eight".