991319921 has 8 divisors (see below), whose sum is σ = 1002797544. Its totient is φ = 979868160.

The previous prime is 991319899. The next prime is 991319939. The reversal of 991319921 is 129913199.

It can be written as a sum of positive squares in 4 ways, for example, as 148230625 + 843089296 = 12175^2 + 29036^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 991319921 - 2¹⁰ = 991318897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991319981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 76751 + ... + 88731.

It is an arithmetic number, because the mean of its divisors is an integer number (125349693).

Almost surely, 2^991319921 is an apocalyptic number.

It is an amenable number.

991319921 is a deficient number, since it is larger than the sum of its proper divisors (11477623).

991319921 is a wasteful number, since it uses less digits than its factorization.

991319921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12931.

The product of its digits is 39366, while the sum is 44.

The square root of 991319921 is about 31485.2333801101. The cubic root of 991319921 is about 997.0982281983.

The spelling of 991319921 in words is "nine hundred ninety-one million, three hundred nineteen thousand, nine hundred twenty-one".