644289840 has 120 divisors (see below), whose sum is σ = 2183163840. Its totient is φ = 170268672.

The previous prime is 644289827. The next prime is 644289871. The reversal of 644289840 is 48982446.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (45).

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 23 ways as a sum of consecutive naturals, for example, 77401 + ... + 85319.

It is an arithmetic number, because the mean of its divisors is an integer number (18193032).

Almost surely, 2^644289840 is an apocalyptic number.

644289840 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 644289840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1091581920).

644289840 is an abundant number, since it is smaller than the sum of its proper divisors (1538874000).

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

644289840 is a wasteful number, since it uses less digits than its factorization.

644289840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8051 (or 8042 counting only the distinct ones).

The product of its (nonzero) digits is 442368, while the sum is 45.

The square root of 644289840 is about 25382.8650865106. The cubic root of 644289840 is about 863.6950441250.

The spelling of 644289840 in words is "six hundred forty-four million, two hundred eighty-nine thousand, eight hundred forty".