9891991999 has 2 divisors, whose sum is σ = 9891992000. Its totient is φ = 9891991998.

The previous prime is 9891991987. The next prime is 9891992039. The reversal of 9891991999 is 9991991989.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 9891991999 - 2¹³ = 9891983807 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9891991969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4945995999 + 4945996000.

It is an arithmetic number, because the mean of its divisors is an integer number (4945996000).

Almost surely, 2^9891991999 is an apocalyptic number.

9891991999 is a deficient number, since it is larger than the sum of its proper divisors (1).

9891991999 is an equidigital number, since it uses as much as digits as its factorization.

9891991999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 38263752, while the sum is 73.

The square root of 9891991999 is about 99458.4938504500. The cubic root of 9891991999 is about 2146.6500561670.

The spelling of 9891991999 in words is "nine billion, eight hundred ninety-one million, nine hundred ninety-one thousand, nine hundred ninety-nine".