1000991991 has 24 divisors (see below), whose sum is σ = 1416192240. Its totient is φ = 628798464.

The previous prime is 1000991923. The next prime is 1000992001. The reversal of 1000991991 is 1991990001.

It is not a de Polignac number, because 1000991991 - 2¹⁹ = 1000467703 is a prime.

It is a super-2 number, since 2×1000991991² = 2003969932092288162, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1000991921) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 206625 + ... + 211413.

It is an arithmetic number, because the mean of its divisors is an integer number (59008010).

Almost surely, 2^1000991991 is an apocalyptic number.

1000991991 is a deficient number, since it is larger than the sum of its proper divisors (415200249).

1000991991 is a wasteful number, since it uses less digits than its factorization.

1000991991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5023 (or 5004 counting only the distinct ones).

The product of its (nonzero) digits is 6561, while the sum is 39.

The square root of 1000991991 is about 31638.4574687199. The cubic root of 1000991991 is about 1000.3305543884.

The spelling of 1000991991 in words is "one billion, nine hundred ninety-one thousand, nine hundred ninety-one".