205317991 has 8 divisors (see below), whose sum is σ = 216871424. Its totient is φ = 194072760.

The previous prime is 205317947. The next prime is 205317997. The reversal of 205317991 is 199713502.

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

It is a de Polignac number, because none of the positive numbers 2^k-205317991 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 205317991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (205317997) 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 7 ways as a sum of consecutive naturals, for example, 75681 + ... + 78346.

It is an arithmetic number, because the mean of its divisors is an integer number (27108928).

Almost surely, 2^205317991 is an apocalyptic number.

205317991 is a deficient number, since it is larger than the sum of its proper divisors (11553433).

205317991 is a wasteful number, since it uses less digits than its factorization.

205317991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154101.

The product of its (nonzero) digits is 17010, while the sum is 37.

The square root of 205317991 is about 14328.9214876766. The cubic root of 205317991 is about 589.9415732625.

The spelling of 205317991 in words is "two hundred five million, three hundred seventeen thousand, nine hundred ninety-one".