644978759040 has 768 divisors, whose sum is σ = 2835930839040. Its totient is φ = 131165798400.

The previous prime is 644978758981. The next prime is 644978759071. The reversal of 644978759040 is 40957879446.

644978759040 is a `hidden beast` number, since 64 + 497 + 87 + 5 + 9 + 0 + 4 + 0 = 666.

It is a super-2 number, since 2×644978759040² (a number of 24 digits) contains 22 as substring.

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 20829970 + ... + 20860910.

It is an arithmetic number, because the mean of its divisors is an integer number (3692618280).

Almost surely, 2^644978759040 is an apocalyptic number.

644978759040 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 644978759040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1417965419520).

644978759040 is an abundant number, since it is smaller than the sum of its proper divisors (2190952080000).

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

644978759040 is a wasteful number, since it uses less digits than its factorization.

644978759040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31031 (or 31016 counting only the distinct ones).

The product of its (nonzero) digits is 60963840, while the sum is 63.

The spelling of 644978759040 in words is "six hundred forty-four billion, nine hundred seventy-eight million, seven hundred fifty-nine thousand, forty".