99891981 has 24 divisors (see below), whose sum is σ = 169362240. Its totient is φ = 57002616.

The previous prime is 99891947. The next prime is 99891989. The reversal of 99891981 is 18919899.

It is not a de Polignac number, because 99891981 - 2⁶ = 99891917 is a prime.

It is a super-2 number, since 2×99891981² = 19956815736208722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99891989) 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, 137040 + ... + 137766.

It is an arithmetic number, because the mean of its divisors is an integer number (7056760).

Almost surely, 2^99891981 is an apocalyptic number.

It is an amenable number.

99891981 is a deficient number, since it is larger than the sum of its proper divisors (69470259).

99891981 is an frugal number, since it uses more digits than its factorization.

99891981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1470 (or 737 counting only the distinct ones).

The product of its digits is 419904, while the sum is 54.

The square root of 99891981 is about 9994.5975906987. The cubic root of 99891981 is about 463.9916965542.

The spelling of 99891981 in words is "ninety-nine million, eight hundred ninety-one thousand, nine hundred eighty-one".