639976821 has 8 divisors (see below), whose sum is σ = 930875424. Its totient is φ = 387864720.

The previous prime is 639976811. The next prime is 639976861. The reversal of 639976821 is 128679936.

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

It is not a de Polignac number, because 639976821 - 2⁷ = 639976693 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639976811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9696586 + ... + 9696651.

It is an arithmetic number, because the mean of its divisors is an integer number (116359428).

Almost surely, 2^639976821 is an apocalyptic number.

It is an amenable number.

639976821 is a deficient number, since it is larger than the sum of its proper divisors (290898603).

639976821 is a wasteful number, since it uses less digits than its factorization.

639976821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19393251.

The product of its digits is 979776, while the sum is 51.

The square root of 639976821 is about 25297.7631619873. The cubic root of 639976821 is about 861.7634722118.

The spelling of 639976821 in words is "six hundred thirty-nine million, nine hundred seventy-six thousand, eight hundred twenty-one".