9891991989 has 12 divisors (see below), whose sum is σ = 15587381472. Its totient is φ = 5995146600.

The previous prime is 9891991987. The next prime is 9891991999.

9891991989 is nontrivially palindromic in base 10.

It is not a de Polignac number, because 9891991989 - 2¹ = 9891991987 is a prime.

It is a super-2 number, since 2×9891991989² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9891991987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 49959457 + ... + 49959654.

It is an arithmetic number, because the mean of its divisors is an integer number (1298948456).

Almost surely, 2^9891991989 is an apocalyptic number.

9891991989 is a gapful number since it is divisible by the number (99) formed by its first and last digit.

It is an amenable number.

9891991989 is a deficient number, since it is larger than the sum of its proper divisors (5695389483).

9891991989 is a wasteful number, since it uses less digits than its factorization.

9891991989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99919128 (or 99919125 counting only the distinct ones).

The product of its digits is 34012224, while the sum is 72.

The square root of 9891991989 is about 99458.4938001778. The cubic root of 9891991989 is about 2146.6500554436.

The spelling of 9891991989 in words is "nine billion, eight hundred ninety-one million, nine hundred ninety-one thousand, nine hundred eighty-nine".