81299965 has 4 divisors (see below), whose sum is σ = 97559964. Its totient is φ = 65039968.

The previous prime is 81299947. The next prime is 81299969. The reversal of 81299965 is 56999218.

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

It can be written as a sum of positive squares in 2 ways, for example, as 61559716 + 19740249 = 7846^2 + 4443^2 .

It is a cyclic number.

It is not a de Polignac number, because 81299965 - 2⁷ = 81299837 is a prime.

It is a Smith number, since the sum of its digits (49) 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 (81299969) 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, 8129992 + ... + 8130001.

It is an arithmetic number, because the mean of its divisors is an integer number (24389991).

Almost surely, 2^81299965 is an apocalyptic number.

It is an amenable number.

81299965 is a deficient number, since it is larger than the sum of its proper divisors (16259999).

81299965 is a wasteful number, since it uses less digits than its factorization.

81299965 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16259998.

The product of its digits is 349920, while the sum is 49.

The square root of 81299965 is about 9016.6493222261. The cubic root of 81299965 is about 433.2083173225.

The spelling of 81299965 in words is "eighty-one million, two hundred ninety-nine thousand, nine hundred sixty-five".