991138660 has 12 divisors (see below), whose sum is σ = 2081391228. Its totient is φ = 396455456.

The previous prime is 991138649. The next prime is 991138669. The reversal of 991138660 is 66831199.

991138660 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 522762496 + 468376164 = 22864^2 + 21642^2 .

It is not an unprimeable number, because it can be changed into a prime (991138669) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 24778447 + ... + 24778486.

It is an arithmetic number, because the mean of its divisors is an integer number (173449269).

Almost surely, 2^991138660 is an apocalyptic number.

It is an amenable number.

991138660 is an abundant number, since it is smaller than the sum of its proper divisors (1090252568).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

991138660 is a wasteful number, since it uses less digits than its factorization.

991138660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49556942 (or 49556940 counting only the distinct ones).

The product of its (nonzero) digits is 69984, while the sum is 43.

The square root of 991138660 is about 31482.3547403939. The cubic root of 991138660 is about 997.0374519763.

The spelling of 991138660 in words is "nine hundred ninety-one million, one hundred thirty-eight thousand, six hundred sixty".