81915913 has 4 divisors (see below), whose sum is σ = 81938560. Its totient is φ = 81893268.

The previous prime is 81915907. The next prime is 81915917. The reversal of 81915913 is 31951918.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81915913 - 2⁵ = 81915881 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81915917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4545 + ... + 13582.

It is an arithmetic number, because the mean of its divisors is an integer number (20484640).

Almost surely, 2^81915913 is an apocalyptic number.

It is an amenable number.

81915913 is a deficient number, since it is larger than the sum of its proper divisors (22647).

81915913 is a wasteful number, since it uses less digits than its factorization.

81915913 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22646.

The product of its digits is 9720, while the sum is 37.

The square root of 81915913 is about 9050.7410193862. The cubic root of 81915913 is about 434.2995959929.

It can be divided in two parts, 81915 and 913, that added together give a palindrome (82828).

The spelling of 81915913 in words is "eighty-one million, nine hundred fifteen thousand, nine hundred thirteen".