99901991 has 4 divisors (see below), whose sum is σ = 114173712. Its totient is φ = 85630272.

The previous prime is 99901987. The next prime is 99901999. The reversal of 99901991 is 19910999.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 99901991 - 2² = 99901987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99901999) 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, 7135850 + ... + 7135863.

It is an arithmetic number, because the mean of its divisors is an integer number (28543428).

Almost surely, 2^99901991 is an apocalyptic number.

99901991 is a deficient number, since it is larger than the sum of its proper divisors (14271721).

99901991 is a wasteful number, since it uses less digits than its factorization.

99901991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14271720.

The product of its (nonzero) digits is 59049, while the sum is 47.

The square root of 99901991 is about 9995.0983486907. The cubic root of 99901991 is about 464.0071946343.

The spelling of 99901991 in words is "ninety-nine million, nine hundred one thousand, nine hundred ninety-one".