81318919 has 4 divisors (see below), whose sum is σ = 88711560. Its totient is φ = 73926280.

The previous prime is 81318911. The next prime is 81318931. The reversal of 81318919 is 91981318.

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 81318919 - 2³ = 81318911 is a prime.

It is a super-2 number, since 2×81318919² = 13225533174657122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81318911) 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, 3696304 + ... + 3696325.

It is an arithmetic number, because the mean of its divisors is an integer number (22177890).

Almost surely, 2^81318919 is an apocalyptic number.

81318919 is a deficient number, since it is larger than the sum of its proper divisors (7392641).

81318919 is a wasteful number, since it uses less digits than its factorization.

81318919 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7392640.

The product of its digits is 15552, while the sum is 40.

The square root of 81318919 is about 9017.7003165996. The cubic root of 81318919 is about 433.2419802826.

The spelling of 81318919 in words is "eighty-one million, three hundred eighteen thousand, nine hundred nineteen".