639981866 has 16 divisors (see below), whose sum is σ = 976578120. Its totient is φ = 314465280.

The previous prime is 639981851. The next prime is 639981871. The reversal of 639981866 is 668189936.

It can be written as a sum of positive squares in 4 ways, for example, as 251064025 + 388917841 = 15845^2 + 19721^2 .

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 229070 + ... + 231846.

Almost surely, 2^639981866 is an apocalyptic number.

639981866 is a deficient number, since it is larger than the sum of its proper divisors (336596254).

639981866 is a wasteful number, since it uses less digits than its factorization.

639981866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4729.

The product of its digits is 3359232, while the sum is 56.

The square root of 639981866 is about 25297.8628741639. The cubic root of 639981866 is about 861.7657366612.

The spelling of 639981866 in words is "six hundred thirty-nine million, nine hundred eighty-one thousand, eight hundred sixty-six".