991921 has 16 divisors (see below), whose sum is σ = 1214208. Its totient is φ = 792000.

The previous prime is 991909. The next prime is 991927. The reversal of 991921 is 129199.

991921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 991921 - 2⁵ = 991889 is a prime.

It is a Duffinian number.

991921 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (991927) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9771 + ... + 9871.

It is an arithmetic number, because the mean of its divisors is an integer number (75888).

2⁹⁹¹⁹²¹ is an apocalyptic number.

It is an amenable number.

991921 is a deficient number, since it is larger than the sum of its proper divisors (222287).

991921 is a wasteful number, since it uses less digits than its factorization.

991921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 192.

The product of its digits is 1458, while the sum is 31.

The square root of 991921 is about 995.9523080951. The cubic root of 991921 is about 99.7299715024.

The spelling of 991921 in words is "nine hundred ninety-one thousand, nine hundred twenty-one".