205999991 has 4 divisors (see below), whose sum is σ = 212645184. Its totient is φ = 199354800.

The previous prime is 205999987. The next prime is 206000059. The reversal of 205999991 is 199999502.

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

It is not a de Polignac number, because 205999991 - 2² = 205999987 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 (205990991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3322550 + ... + 3322611.

It is an arithmetic number, because the mean of its divisors is an integer number (53161296).

Almost surely, 2^205999991 is an apocalyptic number.

205999991 is a deficient number, since it is larger than the sum of its proper divisors (6645193).

205999991 is an equidigital number, since it uses as much as digits as its factorization.

205999991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6645192.

The product of its (nonzero) digits is 590490, while the sum is 53.

The square root of 205999991 is about 14352.6997808775. The cubic root of 205999991 is about 590.5940497616.

The spelling of 205999991 in words is "two hundred five million, nine hundred ninety-nine thousand, nine hundred ninety-one".