991811520 has 672 divisors, whose sum is σ = 4314992640. Its totient is φ = 209848320.

The previous prime is 991811477. The next prime is 991811581. The reversal of 991811520 is 25118199.

It is a tau number, because it is divible by the number of its divisors (672).

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 31993905 + ... + 31993935.

It is an arithmetic number, because the mean of its divisors is an integer number (6421120).

Almost surely, 2^991811520 is an apocalyptic number.

991811520 is a gapful number since it is divisible by the number (90) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 991811520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2157496320).

991811520 is an abundant number, since it is smaller than the sum of its proper divisors (3323181120).

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

991811520 is a wasteful number, since it uses less digits than its factorization.

991811520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110 (or 71 counting only the distinct ones).

The product of its (nonzero) digits is 6480, while the sum is 36.

The square root of 991811520 is about 31493.0392309158. The cubic root of 991811520 is about 997.2630224549.

The spelling of 991811520 in words is "nine hundred ninety-one million, eight hundred eleven thousand, five hundred twenty".