1991111911 has 2 divisors, whose sum is σ = 1991111912. Its totient is φ = 1991111910.

The previous prime is 1991111809. The next prime is 1991111929. The reversal of 1991111911 is 1191111991.

It is a strong prime.

It is an emirp because it is prime and its reverse (1191111991) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 1161111661 and 1661111611.

It is a cyclic number.

It is not a de Polignac number, because 1991111911 - 2⁹ = 1991111399 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991111951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995555955 + 995555956.

It is an arithmetic number, because the mean of its divisors is an integer number (995555956).

Almost surely, 2^1991111911 is an apocalyptic number.

1991111911 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991111911 is an equidigital number, since it uses as much as digits as its factorization.

1991111911 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 729, while the sum is 34.

The square root of 1991111911 is about 44621.8770447860. The cubic root of 1991111911 is about 1258.0518965501.

The spelling of 1991111911 in words is "one billion, nine hundred ninety-one million, one hundred eleven thousand, nine hundred eleven".