644163840 has 432 divisors, whose sum is σ = 2455252800. Its totient is φ = 161243136.

The previous prime is 644163827. The next prime is 644163841. The reversal of 644163840 is 48361446.

644163840 is a `hidden beast` number, since 644 + 1 + 6 + 3 + 8 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (432).

It is a super-3 number, since 3×644163840³ (a number of 27 digits) contains 333 as substring.

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

It is a junction number, because it is equal to n+sod(n) for n = 644163795 and 644163804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644163841) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 5909706 + ... + 5909814.

Almost surely, 2^644163840 is an apocalyptic number.

644163840 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 644163840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1227626400).

644163840 is an abundant number, since it is smaller than the sum of its proper divisors (1811088960).

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

644163840 is a wasteful number, since it uses less digits than its factorization.

644163840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 164 (or 138 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 36.

The square root of 644163840 is about 25380.3829758339. The cubic root of 644163840 is about 863.6387378563.

The spelling of 644163840 in words is "six hundred forty-four million, one hundred sixty-three thousand, eight hundred forty".