991811111 has 2 divisors, whose sum is σ = 991811112. Its totient is φ = 991811110.

The previous prime is 991811099. The next prime is 991811131. The reversal of 991811111 is 111118199.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991811111 is a prime.

It is a Chen prime.

991811111 is a modest number, since divided by 11111 gives 9918 as remainder.

It is equal to p_50452259 and since 991811111 and 50452259 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991811131) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495905555 + 495905556.

It is an arithmetic number, because the mean of its divisors is an integer number (495905556).

Almost surely, 2^991811111 is an apocalyptic number.

991811111 is a deficient number, since it is larger than the sum of its proper divisors (1).

991811111 is an equidigital number, since it uses as much as digits as its factorization.

991811111 is an evil number, because the sum of its binary digits is even.

The product of its digits is 648, while the sum is 32.

The square root of 991811111 is about 31493.0327374167. The cubic root of 991811111 is about 997.2628853721.

The spelling of 991811111 in words is "nine hundred ninety-one million, eight hundred eleven thousand, one hundred eleven".