9991820 has 12 divisors (see below), whose sum is σ = 20982864. Its totient is φ = 3996720.

The previous prime is 9991811. The next prime is 9991837. The reversal of 9991820 is 281999.

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 3 ways as a sum of consecutive naturals, for example, 249776 + ... + 249815.

It is an arithmetic number, because the mean of its divisors is an integer number (1748572).

Almost surely, 2^9991820 is an apocalyptic number.

It is an amenable number.

9991820 is an abundant number, since it is smaller than the sum of its proper divisors (10991044).

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

9991820 is a wasteful number, since it uses less digits than its factorization.

9991820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 499600 (or 499598 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 38.

The square root of 9991820 is about 3160.9840240027. The cubic root of 9991820 is about 215.3847087258.

It can be divided in two parts, 99 and 91820, that added together give a palindrome (91919).

The spelling of 9991820 in words is "nine million, nine hundred ninety-one thousand, eight hundred twenty".