639821977 has 4 divisors (see below), whose sum is σ = 640057140. Its totient is φ = 639586816.

The previous prime is 639821969. The next prime is 639821993. The reversal of 639821977 is 779128936.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 462293001 + 177528976 = 21501^2 + 13324^2 .

It is a cyclic number.

It is not a de Polignac number, because 639821977 - 2³ = 639821969 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639821957) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 113452 + ... + 118957.

It is an arithmetic number, because the mean of its divisors is an integer number (160014285).

Almost surely, 2^639821977 is an apocalyptic number.

It is an amenable number.

639821977 is a deficient number, since it is larger than the sum of its proper divisors (235163).

639821977 is a wasteful number, since it uses less digits than its factorization.

639821977 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 235162.

The product of its digits is 1143072, while the sum is 52.

The square root of 639821977 is about 25294.7025481621. The cubic root of 639821977 is about 861.6939646598.

The spelling of 639821977 in words is "six hundred thirty-nine million, eight hundred twenty-one thousand, nine hundred seventy-seven".