644984640 has 224 divisors, whose sum is σ = 2395728000. Its totient is φ = 162902016.

The previous prime is 644984633. The next prime is 644984647. The reversal of 644984640 is 46489446.

It is an interprime number because it is at equal distance from previous prime (644984633) and next prime (644984647).

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644984647) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 162196 + ... + 166124.

Almost surely, 2^644984640 is an apocalyptic number.

644984640 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 644984640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1197864000).

644984640 is an abundant number, since it is smaller than the sum of its proper divisors (1750743360).

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

644984640 is a wasteful number, since it uses less digits than its factorization.

644984640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3974 (or 3958 counting only the distinct ones).

The product of its (nonzero) digits is 663552, while the sum is 45.

The square root of 644984640 is about 25396.5477968955. The cubic root of 644984640 is about 864.0054012008.

The spelling of 644984640 in words is "six hundred forty-four million, nine hundred eighty-four thousand, six hundred forty".