9991920 has 160 divisors (see below), whose sum is σ = 34283520. Its totient is φ = 2396160.

The previous prime is 9991879. The next prime is 9991939. The reversal of 9991920 is 291999.

It is a happy number.

9991920 is digitally balanced in base 2 and base 4, because in such bases it contains all the possibile digits an equal number of times.

It is a Cunningham number, because it is equal to 3161²-1.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 126441 + ... + 126519.

It is an arithmetic number, because the mean of its divisors is an integer number (214272).

Almost surely, 2^9991920 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 9991920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (17141760).

9991920 is an abundant number, since it is smaller than the sum of its proper divisors (24291600).

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

9991920 is a wasteful number, since it uses less digits than its factorization.

9991920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 143 (or 137 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 39.

The square root of 9991920 is about 3160.9998418222. Note that the first 3 decimals coincide. The cubic root of 9991920 is about 215.3854272602.

The spelling of 9991920 in words is "nine million, nine hundred ninety-one thousand, nine hundred twenty".