991980 has 96 divisors (see below), whose sum is σ = 3386880. Its totient is φ = 239040.

The previous prime is 991979. The next prime is 991981. The reversal of 991980 is 89199.

It is an interprime number because it is at equal distance from previous prime (991979) and next prime (991981).

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

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991980.

It is not an unprimeable number, because it can be changed into a prime (991981) by changing a digit.

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, 5857 + ... + 6023.

It is an arithmetic number, because the mean of its divisors is an integer number (35280).

2⁹⁹¹⁹⁸⁰ is an apocalyptic number.

991980 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 991980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1693440).

991980 is an abundant number, since it is smaller than the sum of its proper divisors (2394900).

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

991980 is a wasteful number, since it uses less digits than its factorization.

991980 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 196 (or 188 counting only the distinct ones).

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

The square root of 991980 is about 995.9819275469. The cubic root of 991980 is about 99.7319487942.

Adding to 991980 its sum of digits (36), we get a square (992016 = 996²).

It can be divided in two parts, 9919 and 80, that added together give a palindrome (9999).

The spelling of 991980 in words is "nine hundred ninety-one thousand, nine hundred eighty".