644312666 has 8 divisors (see below), whose sum is σ = 975022164. Its totient is φ = 319305280.

The previous prime is 644312623. The next prime is 644312671. The reversal of 644312666 is 666213446.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 599221441 + 45091225 = 24479^2 + 6715^2 .

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

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1425245 + ... + 1425696.

Almost surely, 2^644312666 is an apocalyptic number.

644312666 is a deficient number, since it is larger than the sum of its proper divisors (330709498).

644312666 is a wasteful number, since it uses less digits than its factorization.

644312666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2851056.

The product of its digits is 124416, while the sum is 38.

The square root of 644312666 is about 25383.3147165613. The cubic root of 644312666 is about 863.7052437117.

The spelling of 644312666 in words is "six hundred forty-four million, three hundred twelve thousand, six hundred sixty-six".