644886661 has 8 divisors (see below), whose sum is σ = 648090144. Its totient is φ = 641691600.

The previous prime is 644886647. The next prime is 644886679. The reversal of 644886661 is 166688446.

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

It is a cyclic number.

It is not a de Polignac number, because 644886661 - 2⁵ = 644886629 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644886631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 193711 + ... + 197011.

It is an arithmetic number, because the mean of its divisors is an integer number (81011268).

Almost surely, 2^644886661 is an apocalyptic number.

It is an amenable number.

644886661 is a deficient number, since it is larger than the sum of its proper divisors (3203483).

644886661 is a wasteful number, since it uses less digits than its factorization.

644886661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4211.

The product of its digits is 1327104, while the sum is 49.

The square root of 644886661 is about 25394.6187409853. The cubic root of 644886661 is about 863.9616489071.

The spelling of 644886661 in words is "six hundred forty-four million, eight hundred eighty-six thousand, six hundred sixty-one".