81665121 has 4 divisors (see below), whose sum is σ = 108886832. Its totient is φ = 54443412.

The previous prime is 81665117. The next prime is 81665149. The reversal of 81665121 is 12156618.

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 not a de Polignac number, because 81665121 - 2² = 81665117 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81665321) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13610851 + ... + 13610856.

It is an arithmetic number, because the mean of its divisors is an integer number (27221708).

Almost surely, 2^81665121 is an apocalyptic number.

It is an amenable number.

81665121 is a deficient number, since it is larger than the sum of its proper divisors (27221711).

81665121 is a wasteful number, since it uses less digits than its factorization.

81665121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27221710.

The product of its digits is 2880, while the sum is 30.

The square root of 81665121 is about 9036.8756215852. The cubic root of 81665121 is about 433.8559288051.

The spelling of 81665121 in words is "eighty-one million, six hundred sixty-five thousand, one hundred twenty-one".