639648821 has 8 divisors (see below), whose sum is σ = 734493504. Its totient is φ = 545670720.

The previous prime is 639648811. The next prime is 639648829. The reversal of 639648821 is 128846936.

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

It is a de Polignac number, because none of the positive numbers 2^k-639648821 is a prime.

It is a super-2 number, since 2×639648821² = 818301228413380082, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639648829) 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, 215060 + ... + 218013.

It is an arithmetic number, because the mean of its divisors is an integer number (91811688).

Almost surely, 2^639648821 is an apocalyptic number.

It is an amenable number.

639648821 is a deficient number, since it is larger than the sum of its proper divisors (94844683).

639648821 is a wasteful number, since it uses less digits than its factorization.

639648821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 433291.

The product of its digits is 497664, while the sum is 47.

The square root of 639648821 is about 25291.2795445387. The cubic root of 639648821 is about 861.6162237946.

The spelling of 639648821 in words is "six hundred thirty-nine million, six hundred forty-eight thousand, eight hundred twenty-one".