9991921000 has 144 divisors (see below), whose sum is σ = 24439336740. Its totient is φ = 3823545600.

The previous prime is 9991920997. The next prime is 9991921033. The reversal of 9991921000 is 1291999.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

It can be written as a sum of positive squares in 18 ways, for example, as 1365598116 + 8626322884 = 36954^2 + 92878^2 .

It is a Harshad number since it is a multiple of its sum of digits (40).

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 91668946 + ... + 91669054.

Almost surely, 2^9991921000 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 9991921000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (12219668370).

9991921000 is an abundant number, since it is smaller than the sum of its proper divisors (14447415740).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

9991921000 is a wasteful number, since it uses less digits than its factorization.

9991921000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 297 (or 145 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 40.

The square root of 9991921000 is about 99959.5968379225. The cubic root of 9991921000 is about 2153.8543444547.

Multiplying 9991921000 by its sum of digits (40), we get a square (399676840000 = 632200²).

9991921000 divided by its sum of digits (40) gives a square (249798025 = 15805²).

The spelling of 9991921000 in words is "nine billion, nine hundred ninety-one million, nine hundred twenty-one thousand".