991220913 has 24 divisors (see below), whose sum is σ = 1449302400. Its totient is φ = 652770144.

The previous prime is 991220891. The next prime is 991220941. The reversal of 991220913 is 319022199.

It is a happy number.

991220913 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 991220913 - 2⁶ = 991220849 is a prime.

It is not an unprimeable number, because it can be changed into a prime (991220953) 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, 250968 + ... + 254886.

It is an arithmetic number, because the mean of its divisors is an integer number (60387600).

Almost surely, 2^991220913 is an apocalyptic number.

It is an amenable number.

991220913 is a deficient number, since it is larger than the sum of its proper divisors (458081487).

991220913 is a wasteful number, since it uses less digits than its factorization.

991220913 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4261 (or 4258 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 991220913 is about 31483.6610482326. The cubic root of 991220913 is about 997.0650320571.

The spelling of 991220913 in words is "nine hundred ninety-one million, two hundred twenty thousand, nine hundred thirteen".