644646440 has 64 divisors (see below), whose sum is σ = 1535932800. Its totient is φ = 242825472.

The previous prime is 644646439. The next prime is 644646451. The reversal of 644646440 is 44646446.

It is a happy number.

644646440 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (38).

It is a junction number, because it is equal to n+sod(n) for n = 644646394 and 644646403.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 129029 + ... + 133931.

It is an arithmetic number, because the mean of its divisors is an integer number (23998950).

Almost surely, 2^644646440 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 644646440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (767966400).

644646440 is an abundant number, since it is smaller than the sum of its proper divisors (891286360).

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

644646440 is a wasteful number, since it uses less digits than its factorization.

644646440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5106 (or 5102 counting only the distinct ones).

The product of its (nonzero) digits is 221184, while the sum is 38.

The square root of 644646440 is about 25389.8885385501. Note that the first 3 decimals coincide. The cubic root of 644646440 is about 863.8543600252.

The spelling of 644646440 in words is "six hundred forty-four million, six hundred forty-six thousand, four hundred forty".