991131031332221 has 4 divisors (see below), whose sum is σ = 1067371879896252. Its totient is φ = 914890182768192.

The previous prime is 991131031332199. The next prime is 991131031332293. The reversal of 991131031332221 is 122233130131199.

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 56978131204996 + 934152900127225 = 7548386^2 + 30563915^2 .

It is a cyclic number.

It is not a de Polignac number, because 991131031332221 - 2¹⁸ = 991131031070077 is a prime.

It is a super-2 number, since 2×991131031332221² (a number of 31 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991131031332121) 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, 38120424281996 + ... + 38120424282021.

It is an arithmetic number, because the mean of its divisors is an integer number (266842969974063).

Almost surely, 2^{991131031332221} is an apocalyptic number.

It is an amenable number.

991131031332221 is a deficient number, since it is larger than the sum of its proper divisors (76240848564031).

991131031332221 is a wasteful number, since it uses less digits than its factorization.

991131031332221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76240848564030.

The product of its (nonzero) digits is 52488, while the sum is 41.

The spelling of 991131031332221 in words is "nine hundred ninety-one trillion, one hundred thirty-one billion, thirty-one million, three hundred thirty-two thousand, two hundred twenty-one".