99991988 has 24 divisors (see below), whose sum is σ = 182407680. Its totient is φ = 47907360.

The previous prime is 99991987. The next prime is 99991999. The reversal of 99991988 is 88919999.

It is a Harshad number since it is a multiple of its sum of digits (62).

It is a self number, because there is not a number n which added to its sum of digits gives 99991988.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99991981) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8858 + ... + 16686.

It is an arithmetic number, because the mean of its divisors is an integer number (7600320).

Almost surely, 2^99991988 is an apocalyptic number.

It is an amenable number.

99991988 is a deficient number, since it is larger than the sum of its proper divisors (82415692).

99991988 is a wasteful number, since it uses less digits than its factorization.

99991988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7967 (or 7965 counting only the distinct ones).

The product of its digits is 3779136, while the sum is 62.

The square root of 99991988 is about 9999.5993919757. The cubic root of 99991988 is about 464.1464868936.

The spelling of 99991988 in words is "ninety-nine million, nine hundred ninety-one thousand, nine hundred eighty-eight".