644116661 has 2 divisors, whose sum is σ = 644116662. Its totient is φ = 644116660.

The previous prime is 644116639. The next prime is 644116691. The reversal of 644116661 is 166611446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 613800625 + 30316036 = 24775^2 + 5506^2 .

It is a cyclic number.

It is not a de Polignac number, because 644116661 - 2¹⁴ = 644100277 is a prime.

It is a Chen prime.

It is a zygodrome in base 3.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644116691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322058330 + 322058331.

It is an arithmetic number, because the mean of its divisors is an integer number (322058331).

Almost surely, 2^644116661 is an apocalyptic number.

It is an amenable number.

644116661 is a deficient number, since it is larger than the sum of its proper divisors (1).

644116661 is an equidigital number, since it uses as much as digits as its factorization.

644116661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 35.

The square root of 644116661 is about 25379.4535205154. The cubic root of 644116661 is about 863.6176528444.

The spelling of 644116661 in words is "six hundred forty-four million, one hundred sixteen thousand, six hundred sixty-one".