9999999999991 has 8 divisors (see below), whose sum is σ = 10325624864768. Its totient is φ = 9674565399000.

The previous prime is 9999999999971. The next prime is 10000000000037. The reversal of 9999999999991 is 1999999999999.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 9999999999991 - 2⁷ = 9999999999863 is a prime.

It is a super-9 number, since 9×9999999999991⁹ (a number of 118 digits) contains 999999999 as substring.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9999999999971) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 47459115 + ... + 47669356.

It is an arithmetic number, because the mean of its divisors is an integer number (1290703108096).

Almost surely, 2^{9999999999991} is an apocalyptic number.

9999999999991 is a deficient number, since it is larger than the sum of its proper divisors (325624864777).

9999999999991 is a wasteful number, since it uses less digits than its factorization.

9999999999991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 95131893.

The product of its digits is 282429536481, while the sum is 109.

It can be divided in two parts, 999999999999 and 1, that added together give a 12-th power (1000000000000 = 10¹²).

The spelling of 9999999999991 in words is "nine trillion, nine hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".