9891991 has 2 divisors, whose sum is σ = 9891992. Its totient is φ = 9891990.

The previous prime is 9891953. The next prime is 9891997. The reversal of 9891991 is 1991989.

It is a strong prime.

It is an emirp because it is prime and its reverse (1991989) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 9891991 - 2¹³ = 9883799 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9891997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4945995 + 4945996.

It is an arithmetic number, because the mean of its divisors is an integer number (4945996).

Almost surely, 2^9891991 is an apocalyptic number.

9891991 is a deficient number, since it is larger than the sum of its proper divisors (1).

9891991 is an equidigital number, since it uses as much as digits as its factorization.

9891991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 52488, while the sum is 46.

The square root of 9891991 is about 3145.1535733570. The cubic root of 9891991 is about 214.6649983903.

The spelling of 9891991 in words is "nine million, eight hundred ninety-one thousand, nine hundred ninety-one".