99009991 has 2 divisors, whose sum is σ = 99009992. Its totient is φ = 99009990.

The previous prime is 99009971. The next prime is 99010019. The reversal of 99009991 is 19990099.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 99009991 - 2¹⁵ = 98977223 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (99009961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49504995 + 49504996.

It is an arithmetic number, because the mean of its divisors is an integer number (49504996).

Almost surely, 2^99009991 is an apocalyptic number.

99009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

99009991 is an equidigital number, since it uses as much as digits as its factorization.

99009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 59049, while the sum is 46.

The square root of 99009991 is about 9950.3764250404. The cubic root of 99009991 is about 462.6220623529.

It can be divided in two parts, 990099 and 91, that multiplied together give a palindrome (90099009).

The spelling of 99009991 in words is "ninety-nine million, nine thousand, nine hundred ninety-one".