639378666 has 12 divisors (see below), whose sum is σ = 1385320482. Its totient is φ = 213126216.

The previous prime is 639378661. The next prime is 639378713. The reversal of 639378666 is 666873936.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 512343225 + 127035441 = 22635^2 + 11271^2 .

It is not an unprimeable number, because it can be changed into a prime (639378661) 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 5 ways as a sum of consecutive naturals, for example, 17760501 + ... + 17760536.

Almost surely, 2^639378666 is an apocalyptic number.

639378666 is an abundant number, since it is smaller than the sum of its proper divisors (745941816).

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

639378666 is a wasteful number, since it uses less digits than its factorization.

639378666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35521045 (or 35521042 counting only the distinct ones).

The product of its digits is 5878656, while the sum is 54.

The square root of 639378666 is about 25285.9381079682. The cubic root of 639378666 is about 861.4949058145.

The spelling of 639378666 in words is "six hundred thirty-nine million, three hundred seventy-eight thousand, six hundred sixty-six".