644247571968 has 1440 divisors, whose sum is σ = 2638717361280. Its totient is φ = 154255933440.

The previous prime is 644247571901. The next prime is 644247571973. The reversal of 644247571968 is 869175742446.

644247571968 is a `hidden beast` number, since 6 + 4 + 4 + 2 + 475 + 71 + 96 + 8 = 666.

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

Its product of digits (81285120) is a multiple of the sum of its prime factors (810).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 871782543 + ... + 871783281.

It is an arithmetic number, because the mean of its divisors is an integer number (1832442612).

Almost surely, 2^644247571968 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 644247571968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1319358680640).

644247571968 is an abundant number, since it is smaller than the sum of its proper divisors (1994469789312).

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

644247571968 is a wasteful number, since it uses less digits than its factorization.

644247571968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 810 (or 775 counting only the distinct ones).

The product of its digits is 81285120, while the sum is 63.

The spelling of 644247571968 in words is "six hundred forty-four billion, two hundred forty-seven million, five hundred seventy-one thousand, nine hundred sixty-eight".