644255136 has 216 divisors, whose sum is σ = 2164597344. Its totient is φ = 181198080.

The previous prime is 644255123. The next prime is 644255141. The reversal of 644255136 is 631552446.

644255136 is a `hidden beast` number, since 64 + 42 + 551 + 3 + 6 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 644255136.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 1001631 + ... + 1002273.

It is an arithmetic number, because the mean of its divisors is an integer number (10021284).

Almost surely, 2^644255136 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 644255136, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1082298672).

644255136 is an abundant number, since it is smaller than the sum of its proper divisors (1520342208).

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

644255136 is a wasteful number, since it uses less digits than its factorization.

644255136 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 744 (or 726 counting only the distinct ones).

The product of its digits is 86400, while the sum is 36.

The square root of 644255136 is about 25382.1814665328. The cubic root of 644255136 is about 863.6795365024.

The spelling of 644255136 in words is "six hundred forty-four million, two hundred fifty-five thousand, one hundred thirty-six".