561666661 has 2 divisors, whose sum is σ = 561666662. Its totient is φ = 561666660.

The previous prime is 561666653. The next prime is 561666713. The reversal of 561666661 is 166666165.

561666661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 315772900 + 245893761 = 17770^2 + 15681^2 .

It is a cyclic number.

It is not a de Polignac number, because 561666661 - 2³ = 561666653 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (561666641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 280833330 + 280833331.

It is an arithmetic number, because the mean of its divisors is an integer number (280833331).

Almost surely, 2^561666661 is an apocalyptic number.

It is an amenable number.

561666661 is a deficient number, since it is larger than the sum of its proper divisors (1).

561666661 is an equidigital number, since it uses as much as digits as its factorization.

561666661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 233280, while the sum is 43.

The square root of 561666661 is about 23699.5076109188. The cubic root of 561666661 is about 825.0739626374.

The spelling of 561666661 in words is "five hundred sixty-one million, six hundred sixty-six thousand, six hundred sixty-one".