639999994 has 8 divisors (see below), whose sum is σ = 961620660. Its totient is φ = 319459776.

The previous prime is 639999967. The next prime is 640000019. The reversal of 639999994 is 499999936.

It can be written as a sum of positive squares in 2 ways, for example, as 593555769 + 46444225 = 24363^2 + 6815^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 268629 + ... + 271000.

Almost surely, 2^639999994 is an apocalyptic number.

639999994 is a deficient number, since it is larger than the sum of its proper divisors (321620666).

639999994 is a wasteful number, since it uses less digits than its factorization.

639999994 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 540224.

The product of its digits is 38263752, while the sum is 67.

The square root of 639999994 is about 25298.2211627616. The cubic root of 639999994 is about 861.7738733197.

The spelling of 639999994 in words is "six hundred thirty-nine million, nine hundred ninety-nine thousand, nine hundred ninety-four".