90009991 has 4 divisors (see below), whose sum is σ = 90028984. Its totient is φ = 89991000.

The previous prime is 90009943. The next prime is 90010001. The reversal of 90009991 is 19990009.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 90009991 - 2¹³ = 90001799 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 90009991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90009901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4141 + ... + 14041.

It is an arithmetic number, because the mean of its divisors is an integer number (22507246).

Almost surely, 2^90009991 is an apocalyptic number.

90009991 is a deficient number, since it is larger than the sum of its proper divisors (18993).

90009991 is an equidigital number, since it uses as much as digits as its factorization.

90009991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18992.

The product of its (nonzero) digits is 6561, while the sum is 37.

The square root of 90009991 is about 9487.3595378272. The cubic root of 90009991 is about 448.1570568995.

The spelling of 90009991 in words is "ninety million, nine thousand, nine hundred ninety-one".