644215680 has 480 divisors, whose sum is σ = 2500736040. Its totient is φ = 157925376.

The previous prime is 644215643. The next prime is 644215709. The reversal of 644215680 is 86512446.

644215680 is a `hidden beast` number, since 644 + 2 + 1 + 5 + 6 + 8 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (480).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 14981739 + ... + 14981781.

Almost surely, 2^644215680 is an apocalyptic number.

644215680 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 644215680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1250368020).

644215680 is an abundant number, since it is smaller than the sum of its proper divisors (1856520360).

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

644215680 is a wasteful number, since it uses less digits than its factorization.

644215680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 108 (or 70 counting only the distinct ones).

The product of its (nonzero) digits is 46080, while the sum is 36.

The square root of 644215680 is about 25381.4042164731. The cubic root of 644215680 is about 863.6619047529.

It can be divided in two parts, 6442 and 15680, that added together give a palindrome (22122).

The spelling of 644215680 in words is "six hundred forty-four million, two hundred fifteen thousand, six hundred eighty".