9981 has 6 divisors (see below), whose sum is σ = 14430. Its totient is φ = 6648.

The previous prime is 9973. The next prime is 10007. The reversal of 9981 is 1899.

It can be written as a sum of positive squares in only one way, i.e., 5625 + 4356 = 75^2 + 66^2 .

It is not a de Polignac number, because 9981 - 2³ = 9973 is a prime.

It is a super-2 number, since 2×9981² = 199240722, which contains 22 as substring.

It is a Curzon number.

It is a plaindrome in base 14.

It is a nialpdrome in base 10 and base 11.

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 9981.

It is not an unprimeable number, because it can be changed into a prime (9901) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 546 + ... + 563.

It is an arithmetic number, because the mean of its divisors is an integer number (2405).

2⁹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

9981 is a deficient number, since it is larger than the sum of its proper divisors (4449).

9981 is a wasteful number, since it uses less digits than its factorization.

9981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1115 (or 1112 counting only the distinct ones).

The product of its digits is 648, while the sum is 27.

The square root of 9981 is about 99.9049548321. The cubic root of 9981 is about 21.5306934965.

It can be divided in two parts, 998 and 1, that added together give a palindrome (999).

The spelling of 9981 in words is "nine thousand, nine hundred eighty-one".