9991801680 has 960 divisors, whose sum is σ = 41550340608. Its totient is φ = 1968046080.

The previous prime is 9991801679. The next prime is 9991801709. The reversal of 9991801680 is 861081999.

It is a happy number.

It is a Cunningham number, because it is equal to 99959²-1.

It is a super-2 number, since 2×9991801680² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (51).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 188524534 + ... + 188524586.

Almost surely, 2^9991801680 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 9991801680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (20775170304).

9991801680 is an abundant number, since it is smaller than the sum of its proper divisors (31558538928).

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

9991801680 is a wasteful number, since it uses less digits than its factorization.

9991801680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 164 (or 151 counting only the distinct ones).

The product of its (nonzero) digits is 279936, while the sum is 51.

The square root of 9991801680 is about 99958.9999949979. Note that the first 5 decimals coincide. The cubic root of 9991801680 is about 2153.8457708974.

The spelling of 9991801680 in words is "nine billion, nine hundred ninety-one million, eight hundred one thousand, six hundred eighty".