991821289 has 4 divisors (see below), whose sum is σ = 1005407956. Its totient is φ = 978234624.

The previous prime is 991821287. The next prime is 991821317. The reversal of 991821289 is 982128199.

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

It can be written as a sum of positive squares in 2 ways, for example, as 453349264 + 538472025 = 21292^2 + 23205^2 .

It is a cyclic number.

It is not a de Polignac number, because 991821289 - 2¹ = 991821287 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991821287) 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, 6793224 + ... + 6793369.

It is an arithmetic number, because the mean of its divisors is an integer number (251351989).

Almost surely, 2^991821289 is an apocalyptic number.

It is an amenable number.

991821289 is a deficient number, since it is larger than the sum of its proper divisors (13586667).

991821289 is a wasteful number, since it uses less digits than its factorization.

991821289 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13586666.

The product of its digits is 186624, while the sum is 49.

The square root of 991821289 is about 31493.1943282989. The cubic root of 991821289 is about 997.2662966759.

The spelling of 991821289 in words is "nine hundred ninety-one million, eight hundred twenty-one thousand, two hundred eighty-nine".