1191111991 has 2 divisors, whose sum is σ = 1191111992. Its totient is φ = 1191111990.

The previous prime is 1191111947. The next prime is 1191112037. The reversal of 1191111991 is 1991111911.

It is a weak prime.

It is an emirp because it is prime and its reverse (1991111911) is a distict prime. It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 1661111611 and 1161111661.

It is a cyclic number.

It is not a de Polignac number, because 1191111991 - 2¹⁹ = 1190587703 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1191111091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 595555995 + 595555996.

It is an arithmetic number, because the mean of its divisors is an integer number (595555996).

Almost surely, 2^1191111991 is an apocalyptic number.

1191111991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1191111991 is an equidigital number, since it uses as much as digits as its factorization.

1191111991 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 1191111991 is about 34512.4903621863. The cubic root of 1191111991 is about 1060.0284764511.

The spelling of 1191111991 in words is "one billion, one hundred ninety-one million, one hundred eleven thousand, nine hundred ninety-one".