208991 has 2 divisors, whose sum is σ = 208992. Its totient is φ = 208990.

The previous prime is 208963. The next prime is 208993. The reversal of 208991 is 199802.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 208991 - 2⁶ = 208927 is a prime.

It is a Sophie Germain prime.

Together with 208993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (208993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104495 + 104496.

It is an arithmetic number, because the mean of its divisors is an integer number (104496).

2²⁰⁸⁹⁹¹ is an apocalyptic number.

208991 is a deficient number, since it is larger than the sum of its proper divisors (1).

208991 is an equidigital number, since it uses as much as digits as its factorization.

208991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 29.

The square root of 208991 is about 457.1553346511. The cubic root of 208991 is about 59.3438695537.

The spelling of 208991 in words is "two hundred eight thousand, nine hundred ninety-one".