208717991 has 2 divisors, whose sum is σ = 208717992. Its totient is φ = 208717990.

The previous prime is 208717981. The next prime is 208717997. The reversal of 208717991 is 199717802.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-208717991 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (208717997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104358995 + 104358996.

It is an arithmetic number, because the mean of its divisors is an integer number (104358996).

Almost surely, 2^208717991 is an apocalyptic number.

208717991 is a deficient number, since it is larger than the sum of its proper divisors (1).

208717991 is an equidigital number, since it uses as much as digits as its factorization.

208717991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 63504, while the sum is 44.

The square root of 208717991 is about 14447.0755172111. The cubic root of 208717991 is about 593.1801761053.

The spelling of 208717991 in words is "two hundred eight million, seven hundred seventeen thousand, nine hundred ninety-one".