991100081 has 2 divisors, whose sum is σ = 991100082. Its totient is φ = 991100080.

The previous prime is 991099973. The next prime is 991100083. The reversal of 991100081 is 180001199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 971880625 + 19219456 = 31175^2 + 4384^2 .

It is a cyclic number.

It is not a de Polignac number, because 991100081 - 2¹⁸ = 990837937 is a prime.

It is a super-2 number, since 2×991100081² = 1964558741116413122, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 991100083, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (991100083) 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 as a sum of consecutive naturals, namely, 495550040 + 495550041.

It is an arithmetic number, because the mean of its divisors is an integer number (495550041).

Almost surely, 2^991100081 is an apocalyptic number.

It is an amenable number.

991100081 is a deficient number, since it is larger than the sum of its proper divisors (1).

991100081 is an equidigital number, since it uses as much as digits as its factorization.

991100081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 29.

The square root of 991100081 is about 31481.7420261332. The cubic root of 991100081 is about 997.0245156071.

The spelling of 991100081 in words is "nine hundred ninety-one million, one hundred thousand, eighty-one".