1991011111 has 2 divisors, whose sum is σ = 1991011112. Its totient is φ = 1991011110.

The previous prime is 1991011073. The next prime is 1991011129. The reversal of 1991011111 is 1111101991.

It is a strong prime.

It is an emirp because it is prime and its reverse (1111101991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1991011111 - 2¹³ = 1991002919 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991011411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995505555 + 995505556.

It is an arithmetic number, because the mean of its divisors is an integer number (995505556).

Almost surely, 2^1991011111 is an apocalyptic number.

1991011111 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991011111 is an equidigital number, since it uses as much as digits as its factorization.

1991011111 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 81, while the sum is 25.

The square root of 1991011111 is about 44620.7475396816. The cubic root of 1991011111 is about 1258.0306665746.

The spelling of 1991011111 in words is "one billion, nine hundred ninety-one million, eleven thousand, one hundred eleven".