991332720 has 180 divisors, whose sum is σ = 3872910600. Its totient is φ = 226582272.

The previous prime is 991332689. The next prime is 991332757. The reversal of 991332720 is 27233199.

It is a tau number, because it is divible by the number of its divisors (180).

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 polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 21231 + ... + 49329.

It is an arithmetic number, because the mean of its divisors is an integer number (21516170).

Almost surely, 2^991332720 is an apocalyptic number.

991332720 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 991332720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1936455300).

991332720 is an abundant number, since it is smaller than the sum of its proper divisors (2881577880).

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

991332720 is a wasteful number, since it uses less digits than its factorization.

991332720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28132 (or 28116 counting only the distinct ones).

The product of its (nonzero) digits is 20412, while the sum is 36.

The square root of 991332720 is about 31485.4366334660. The cubic root of 991332720 is about 997.1025193812.

The spelling of 991332720 in words is "nine hundred ninety-one million, three hundred thirty-two thousand, seven hundred twenty".