991189219921 has 8 divisors (see below), whose sum is σ = 1000585573704. Its totient is φ = 981803827200.

The previous prime is 991189219897. The next prime is 991189219931. The reversal of 991189219921 is 129912981199.

It can be written as a sum of positive squares in 4 ways, for example, as 418686643600 + 572502576321 = 647060^2 + 756639^2 .

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 991189219921 - 2⁹ = 991189219409 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 991189219921.

It is not an unprimeable number, because it can be changed into a prime (991189219931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2558496 + ... + 2920321.

It is an arithmetic number, because the mean of its divisors is an integer number (125073196713).

Almost surely, 2^991189219921 is an apocalyptic number.

It is an amenable number.

991189219921 is a deficient number, since it is larger than the sum of its proper divisors (9396353783).

991189219921 is a wasteful number, since it uses less digits than its factorization.

991189219921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5480531.

The product of its digits is 1889568, while the sum is 61.

The spelling of 991189219921 in words is "nine hundred ninety-one billion, one hundred eighty-nine million, two hundred nineteen thousand, nine hundred twenty-one".