644345399880 has 1536 divisors, whose sum is σ = 2819296972800. Its totient is φ = 131211601920.

The previous prime is 644345399833. The next prime is 644345399891. The reversal of 644345399880 is 88993543446.

644345399880 is a `hidden beast` number, since 6 + 4 + 4 + 3 + 4 + 539 + 98 + 8 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 383 ways as a sum of consecutive naturals, for example, 1727467374 + ... + 1727467746.

It is an arithmetic number, because the mean of its divisors is an integer number (1835479800).

Almost surely, 2^644345399880 is an apocalyptic number.

644345399880 is a gapful number since it is divisible by the number (60) 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 644345399880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1409648486400).

644345399880 is an abundant number, since it is smaller than the sum of its proper divisors (2174951572920).

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

644345399880 is a wasteful number, since it uses less digits than its factorization.

644345399880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 463 (or 434 counting only the distinct ones).

The product of its (nonzero) digits is 89579520, while the sum is 63.

The spelling of 644345399880 in words is "six hundred forty-four billion, three hundred forty-five million, three hundred ninety-nine thousand, eight hundred eighty".