991806191 has 2 divisors, whose sum is σ = 991806192. Its totient is φ = 991806190.

The previous prime is 991806149. The next prime is 991806199. The reversal of 991806191 is 191608199.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991806191 - 2¹⁰ = 991805167 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991806199) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495903095 + 495903096.

It is an arithmetic number, because the mean of its divisors is an integer number (495903096).

Almost surely, 2^991806191 is an apocalyptic number.

991806191 is a deficient number, since it is larger than the sum of its proper divisors (1).

991806191 is an equidigital number, since it uses as much as digits as its factorization.

991806191 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 34992, while the sum is 44.

The square root of 991806191 is about 31492.9546248046. The cubic root of 991806191 is about 997.2612363547.

The spelling of 991806191 in words is "nine hundred ninety-one million, eight hundred six thousand, one hundred ninety-one".