639999990 has 192 divisors, whose sum is σ = 2022359040. Its totient is φ = 137168640.

The previous prime is 639999967. The next prime is 640000019. The reversal of 639999990 is 99999936.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1519980 + ... + 1520400.

It is an arithmetic number, because the mean of its divisors is an integer number (10533120).

Almost surely, 2^639999990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639999990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1011179520).

639999990 is an abundant number, since it is smaller than the sum of its proper divisors (1382359050).

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

639999990 is a wasteful number, since it uses less digits than its factorization.

639999990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 587 (or 584 counting only the distinct ones).

The product of its (nonzero) digits is 9565938, while the sum is 63.

The square root of 639999990 is about 25298.2210837047. The cubic root of 639999990 is about 861.7738715243.

The spelling of 639999990 in words is "six hundred thirty-nine million, nine hundred ninety-nine thousand, nine hundred ninety".