81919999 has 8 divisors (see below), whose sum is σ = 93721760. Its totient is φ = 70142976.

The previous prime is 81919993. The next prime is 81920021. The reversal of 81919999 is 99991918.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81919999 - 2⁵ = 81919967 is a prime.

It is a Duffinian number.

81919999 is a modest number, since divided by 9999 gives 8191 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81919993) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1567 + ... + 12895.

It is an arithmetic number, because the mean of its divisors is an integer number (11715220).

Almost surely, 2^81919999 is an apocalyptic number.

81919999 is a deficient number, since it is larger than the sum of its proper divisors (11801761).

81919999 is a wasteful number, since it uses less digits than its factorization.

81919999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12369.

The product of its digits is 472392, while the sum is 55.

The square root of 81919999 is about 9050.9667439451. The cubic root of 81919999 is about 434.3068168880.

The spelling of 81919999 in words is "eighty-one million, nine hundred nineteen thousand, nine hundred ninety-nine".