9991801681 has 9 divisors (see below), whose sum is σ = 10547368923. Its totient is φ = 9464118120.

The previous prime is 9991801679. The next prime is 9991801709. The reversal of 9991801681 is 1861081999.

The square root of 9991801681 is 99959.

It is a perfect power (a square), and thus also a powerful number.

9991801681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 7437510081 + 2554291600 = 86241^2 + 50540^2 .

It is not a de Polignac number, because 9991801681 - 2¹ = 9991801679 is a prime.

It is a super-2 number, since 2×9991801681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (9991801661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1896591 + ... + 1901851.

Almost surely, 2^9991801681 is an apocalyptic number.

9991801681 is the 99959-th square number.

9991801681 is the 49980-th centered octagonal number.

It is an amenable number.

9991801681 is a deficient number, since it is larger than the sum of its proper divisors (555567242).

9991801681 is an frugal number, since it uses more digits than its factorization.

9991801681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10560 (or 5280 counting only the distinct ones).

The product of its (nonzero) digits is 279936, while the sum is 52.

The cubic root of 9991801681 is about 2153.8457709692.

The spelling of 9991801681 in words is "nine billion, nine hundred ninety-one million, eight hundred one thousand, six hundred eighty-one".