99999981 has 8 divisors (see below), whose sum is σ = 148148160.
Its totient is φ = 66666636.
The previous prime is 99999971. The next prime is 99999989. The reversal of 99999981 is 18999999.
It can be divided in two parts, 9999998 and 1, that added together give a palindrome (9999999).
It is not a de Polignac number, because 99999981 - 213 = 99991789 is a prime.
It is a super-2 number, since 2×999999812 = 19999992400000722, which contains 22 as substring.
It is a Curzon number.
It is a nialpdrome in base 10.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (99999989) 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 7 ways as a sum of consecutive naturals, for example, 1851825 + ... + 1851878.
It is an arithmetic number, because the mean of its divisors is an integer number (18518520).
Almost surely, 299999981 is an apocalyptic number.
It is an amenable number.
99999981 is a deficient number, since it is larger than the sum of its proper divisors (48148179).
99999981 is a wasteful number, since it uses less digits than its factorization.
99999981 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 3703712 (or 3703706 counting only the distinct ones).
The product of its digits is 4251528, while the sum is 63.
The square root of 99999981 is about 9999.9990500000.
Note that the first 3 decimals coincide.
The cubic root of 99999981 is about 464.1588539645.
The spelling of 99999981 in words is "ninety-nine million, nine hundred ninety-nine thousand, nine hundred eighty-one".