640006666 has 16 divisors (see below), whose sum is σ = 1034749800. Its totient is φ = 295132608.

The previous prime is 640006651. The next prime is 640006777. The reversal of 640006666 is 666600046.

It can be written as a sum of positive squares in 4 ways, for example, as 553237441 + 86769225 = 23521^2 + 9315^2 .

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, 21940 + ... + 41968.

Almost surely, 2^640006666 is an apocalyptic number.

640006666 is a deficient number, since it is larger than the sum of its proper divisors (394743134).

640006666 is a wasteful number, since it uses less digits than its factorization.

640006666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21273.

The product of its (nonzero) digits is 31104, while the sum is 34.

The square root of 640006666 is about 25298.3530293970. The cubic root of 640006666 is about 861.7768679735.

The spelling of 640006666 in words is "six hundred forty million, six thousand, six hundred sixty-six".