99981 has 24 divisors (see below), whose sum is σ = 176960. Its totient is φ = 54648.

The previous prime is 99971. The next prime is 99989. The reversal of 99981 is 18999.

It is not a de Polignac number, because 99981 - 2⁹ = 99469 is a prime.

It is a super-2 number, since 2×99981² = 19992400722, which contains 22 as substring.

It is a plaindrome in base 13.

It is a nialpdrome in base 10.

It is a zygodrome in base 5.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99989) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4336 + ... + 4358.

2⁹⁹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

99981 is a deficient number, since it is larger than the sum of its proper divisors (76979).

99981 is a wasteful number, since it uses less digits than its factorization.

99981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62 (or 33 counting only the distinct ones).

The product of its digits is 5832, while the sum is 36.

The square root of 99981 is about 316.1977229520. The cubic root of 99981 is about 46.4129484770.

Subtracting from 99981 its product of digits (5832), we obtain a palindrome (94149).

It can be divided in two parts, 9998 and 1, that added together give a palindrome (9999).

The spelling of 99981 in words is "ninety-nine thousand, nine hundred eighty-one".