99909991 has 2 divisors, whose sum is σ = 99909992. Its totient is φ = 99909990.

The previous prime is 99909973. The next prime is 99910001. The reversal of 99909991 is 19990999.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 99909991 - 2⁷ = 99909863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (99909791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49954995 + 49954996.

It is an arithmetic number, because the mean of its divisors is an integer number (49954996).

Almost surely, 2^99909991 is an apocalyptic number.

99909991 is a deficient number, since it is larger than the sum of its proper divisors (1).

99909991 is an equidigital number, since it uses as much as digits as its factorization.

99909991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 531441, while the sum is 55.

The square root of 99909991 is about 9995.4985368415. The cubic root of 99909991 is about 464.0195799679.

The spelling of 99909991 in words is "ninety-nine million, nine hundred nine thousand, nine hundred ninety-one".