991108991 has 2 divisors, whose sum is σ = 991108992. Its totient is φ = 991108990.

The previous prime is 991108961. The next prime is 991109011. The reversal of 991108991 is 199801199.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991108991 - 2¹⁰ = 991107967 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991108961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495554495 + 495554496.

It is an arithmetic number, because the mean of its divisors is an integer number (495554496).

Almost surely, 2^991108991 is an apocalyptic number.

991108991 is a deficient number, since it is larger than the sum of its proper divisors (1).

991108991 is an equidigital number, since it uses as much as digits as its factorization.

991108991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 52488, while the sum is 47.

The square root of 991108991 is about 31481.8835364087. The cubic root of 991108991 is about 997.0275033517.

The spelling of 991108991 in words is "nine hundred ninety-one million, one hundred eight thousand, nine hundred ninety-one".