991921104 has 120 divisors (see below), whose sum is σ = 2890428840. Its totient is φ = 317162496.

The previous prime is 991921103. The next prime is 991921111. The reversal of 991921104 is 401129199.

It can be written as a sum of positive squares in 4 ways, for example, as 687488400 + 304432704 = 26220^2 + 17448^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991921103) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 721762 + ... + 723134.

It is an arithmetic number, because the mean of its divisors is an integer number (24086907).

Almost surely, 2^991921104 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 991921104, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1445214420).

991921104 is an abundant number, since it is smaller than the sum of its proper divisors (1898507736).

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

991921104 is a wasteful number, since it uses less digits than its factorization.

991921104 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1589 (or 1580 counting only the distinct ones).

The product of its (nonzero) digits is 5832, while the sum is 36.

The square root of 991921104 is about 31494.7789958907. The cubic root of 991921104 is about 997.2997498788.

The spelling of 991921104 in words is "nine hundred ninety-one million, nine hundred twenty-one thousand, one hundred four".