991111680 has 320 divisors, whose sum is σ = 3794757120. Its totient is φ = 243744768.

The previous prime is 991111669. The next prime is 991111721. The reversal of 991111680 is 86111199.

It is a tau number, because it is divible by the number of its divisors (320).

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

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 898009 + ... + 899111.

It is an arithmetic number, because the mean of its divisors is an integer number (11858616).

Almost surely, 2^991111680 is an apocalyptic number.

991111680 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 991111680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1897378560).

991111680 is an abundant number, since it is smaller than the sum of its proper divisors (2803645440).

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

991111680 is a wasteful number, since it uses less digits than its factorization.

991111680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1148 (or 1126 counting only the distinct ones).

The product of its (nonzero) digits is 3888, while the sum is 36.

The square root of 991111680 is about 31481.9262434814. The cubic root of 991111680 is about 997.0284050368.

The spelling of 991111680 in words is "nine hundred ninety-one million, one hundred eleven thousand, six hundred eighty".