205686661 has 4 divisors (see below), whose sum is σ = 206418924. Its totient is φ = 204954400.

The previous prime is 205686653. The next prime is 205686667. The reversal of 205686661 is 166686502.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 165122500 + 40564161 = 12850^2 + 6369^2 .

It is a cyclic number.

It is not a de Polignac number, because 205686661 - 2³ = 205686653 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (205686667) 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 3 ways as a sum of consecutive naturals, for example, 365710 + ... + 366271.

It is an arithmetic number, because the mean of its divisors is an integer number (51604731).

Almost surely, 2^205686661 is an apocalyptic number.

It is an amenable number.

205686661 is a deficient number, since it is larger than the sum of its proper divisors (732263).

205686661 is an equidigital number, since it uses as much as digits as its factorization.

205686661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 732262.

The product of its (nonzero) digits is 103680, while the sum is 40.

The square root of 205686661 is about 14341.7802590892. The cubic root of 205686661 is about 590.2944627987.

The spelling of 205686661 in words is "two hundred five million, six hundred eighty-six thousand, six hundred sixty-one".