640631394 has 96 divisors (see below), whose sum is σ = 1561660464. Its totient is φ = 188490240.

The previous prime is 640631309. The next prime is 640631413. The reversal of 640631394 is 493136046.

640631394 is a `hidden beast` number, since 640 + 6 + 3 + 1 + 3 + 9 + 4 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 31775769 + 608855625 = 5637^2 + 24675^2 .

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Curzon number.

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 47 ways as a sum of consecutive naturals, for example, 527532 + ... + 528744.

Almost surely, 2^640631394 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640631394, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (780830232).

640631394 is an abundant number, since it is smaller than the sum of its proper divisors (921029070).

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

640631394 is a wasteful number, since it uses less digits than its factorization.

640631394 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1332 (or 1329 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 36.

The square root of 640631394 is about 25310.6972246914. The cubic root of 640631394 is about 862.0571781058.

The spelling of 640631394 in words is "six hundred forty million, six hundred thirty-one thousand, three hundred ninety-four".