644105666 has 8 divisors (see below), whose sum is σ = 970305804. Its totient is φ = 320670400.

The previous prime is 644105663. The next prime is 644105669. The reversal of 644105666 is 666501446.

It is an interprime number because it is at equal distance from previous prime (644105663) and next prime (644105669).

It can be written as a sum of positive squares in 2 ways, for example, as 622752025 + 21353641 = 24955^2 + 4621^2 .

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

It is not an unprimeable number, because it can be changed into a prime (644105663) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 690635 + ... + 691566.

Almost surely, 2^644105666 is an apocalyptic number.

644105666 is a deficient number, since it is larger than the sum of its proper divisors (326200138).

644105666 is a wasteful number, since it uses less digits than its factorization.

644105666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1382436.

The product of its (nonzero) digits is 103680, while the sum is 38.

The square root of 644105666 is about 25379.2369073619. The cubic root of 644105666 is about 863.6127388639.

The spelling of 644105666 in words is "six hundred forty-four million, one hundred five thousand, six hundred sixty-six".