639908640 has 288 divisors, whose sum is σ = 2606204160. Its totient is φ = 146216448.

The previous prime is 639908623. The next prime is 639908641. The reversal of 639908640 is 46809936.

639908640 is a `hidden beast` number, since 639 + 9 + 0 + 8 + 6 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

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

It is not an unprimeable number, because it can be changed into a prime (639908641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 210169 + ... + 213191.

It is an arithmetic number, because the mean of its divisors is an integer number (9049320).

Almost surely, 2^639908640 is an apocalyptic number.

639908640 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 639908640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1303102080).

639908640 is an abundant number, since it is smaller than the sum of its proper divisors (1966295520).

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

639908640 is a wasteful number, since it uses less digits than its factorization.

639908640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3061 (or 3040 counting only the distinct ones).

The product of its (nonzero) digits is 279936, while the sum is 45.

The square root of 639908640 is about 25296.4155563590. The cubic root of 639908640 is about 861.7328679878.

The spelling of 639908640 in words is "six hundred thirty-nine million, nine hundred eight thousand, six hundred forty".