644130640 has 80 divisors (see below), whose sum is σ = 1569506688. Its totient is φ = 245380608.

The previous prime is 644130601. The next prime is 644130661. The reversal of 644130640 is 46031446.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is a junction number, because it is equal to n+sod(n) for n = 644130599 and 644130608.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 520102 + ... + 521338.

Almost surely, 2^644130640 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 644130640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (784753344).

644130640 is an abundant number, since it is smaller than the sum of its proper divisors (925376048).

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

644130640 is a wasteful number, since it uses less digits than its factorization.

644130640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1556 (or 1550 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 28.

The square root of 644130640 is about 25379.7289189621. The cubic root of 644130640 is about 863.6239003792.

The spelling of 644130640 in words is "six hundred forty-four million, one hundred thirty thousand, six hundred forty".