639931656 has 128 divisors (see below), whose sum is σ = 1987211520. Its totient is φ = 167215104.

The previous prime is 639931639. The next prime is 639931681. The reversal of 639931656 is 656139936.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 245496 + ... + 248088.

It is an arithmetic number, because the mean of its divisors is an integer number (15525090).

Almost surely, 2^639931656 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 639931656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (993605760).

639931656 is an abundant number, since it is smaller than the sum of its proper divisors (1347279864).

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

639931656 is a wasteful number, since it uses less digits than its factorization.

639931656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2735 (or 2731 counting only the distinct ones).

The product of its digits is 787320, while the sum is 48.

The square root of 639931656 is about 25296.8704783813. The cubic root of 639931656 is about 861.7431993615.

It can be divided in two parts, 639 and 931656, that added together give a triangular number (932295 = T₁₃₆₅).

The spelling of 639931656 in words is "six hundred thirty-nine million, nine hundred thirty-one thousand, six hundred fifty-six".