991099 has 4 divisors (see below), whose sum is σ = 996480. Its totient is φ = 985720.

The previous prime is 991091. The next prime is 991127. The reversal of 991099 is 990199.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 991099 - 2³ = 991091 is a prime.

It is a Duffinian number.

991099 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (991091) 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, 2404 + ... + 2785.

It is an arithmetic number, because the mean of its divisors is an integer number (249120).

2⁹⁹¹⁰⁹⁹ is an apocalyptic number.

991099 is a deficient number, since it is larger than the sum of its proper divisors (5381).

991099 is a wasteful number, since it uses less digits than its factorization.

991099 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5380.

The product of its (nonzero) digits is 6561, while the sum is 37.

The square root of 991099 is about 995.5395522027. The cubic root of 991099 is about 99.7024153120.

Subtracting from 991099 its reverse (990199), we obtain a square (900 = 30²).

It can be divided in two parts, 99 and 1099, that multiplied together give a palindrome (108801).

The spelling of 991099 in words is "nine hundred ninety-one thousand, ninety-nine".