91999999 has 12 divisors (see below), whose sum is σ = 115253544. Its totient is φ = 72790704.

The previous prime is 91999993. The next prime is 92000011. The reversal of 91999999 is 99999919.

It is not a de Polignac number, because 91999999 - 2⁹ = 91999487 is a prime.

91999999 is a modest number, since divided by 9999 gives 9199 as remainder.

It is a plaindrome in base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 91999999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91999993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 71577 + ... + 72850.

It is an arithmetic number, because the mean of its divisors is an integer number (9604462).

Almost surely, 2^91999999 is an apocalyptic number.

91999999 is a deficient number, since it is larger than the sum of its proper divisors (23253545).

91999999 is a wasteful number, since it uses less digits than its factorization.

91999999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 144454 (or 144447 counting only the distinct ones).

The product of its digits is 4782969, while the sum is 64.

The square root of 91999999 is about 9591.6629944968. The cubic root of 91999999 is about 451.4357419118.

It can be divided in two parts, 91 and 999999, that multiplied together give a palindrome (90999909).

The spelling of 91999999 in words is "ninety-one million, nine hundred ninety-nine thousand, nine hundred ninety-nine".