1091991009 has 32 divisors (see below), whose sum is σ = 1559347200. Its totient is φ = 677738880.

The previous prime is 1091991001. The next prime is 1091991011. The reversal of 1091991009 is 9001991901.

It is not a de Polignac number, because 1091991009 - 2³ = 1091991001 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1091991001) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1264912 + ... + 1265774.

It is an arithmetic number, because the mean of its divisors is an integer number (48729600).

Almost surely, 2^1091991009 is an apocalyptic number.

1091991009 is a gapful number since it is divisible by the number (19) formed by its first and last digit.

It is an amenable number.

1091991009 is a deficient number, since it is larger than the sum of its proper divisors (467356191).

1091991009 is a wasteful number, since it uses less digits than its factorization.

1091991009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1245.

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

The square root of 1091991009 is about 33045.2872434179. The cubic root of 1091991009 is about 1029.7687006942.

The spelling of 1091991009 in words is "one billion, ninety-one million, nine hundred ninety-one thousand, nine".