81917399 has 4 divisors (see below), whose sum is σ = 82229136. Its totient is φ = 81605664.

The previous prime is 81917393. The next prime is 81917447. The reversal of 81917399 is 99371918.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 81917399 - 2²⁴ = 65140183 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 (81917393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 155474 + ... + 155999.

It is an arithmetic number, because the mean of its divisors is an integer number (20557284).

Almost surely, 2^81917399 is an apocalyptic number.

81917399 is a deficient number, since it is larger than the sum of its proper divisors (311737).

81917399 is a wasteful number, since it uses less digits than its factorization.

81917399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311736.

The product of its digits is 122472, while the sum is 47.

The square root of 81917399 is about 9050.8231117396. The cubic root of 81917399 is about 434.3022221220.

The spelling of 81917399 in words is "eighty-one million, nine hundred seventeen thousand, three hundred ninety-nine".