81972505 has 4 divisors (see below), whose sum is σ = 98367012. Its totient is φ = 65578000.

The previous prime is 81972497. The next prime is 81972511. The reversal of 81972505 is 50527918.

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 65415744 + 16556761 = 8088^2 + 4069^2 .

It is not a de Polignac number, because 81972505 - 2³ = 81972497 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 8197246 + ... + 8197255.

It is an arithmetic number, because the mean of its divisors is an integer number (24591753).

Almost surely, 2^81972505 is an apocalyptic number.

It is an amenable number.

81972505 is a deficient number, since it is larger than the sum of its proper divisors (16394507).

81972505 is a wasteful number, since it uses less digits than its factorization.

81972505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16394506.

The product of its (nonzero) digits is 25200, while the sum is 37.

The square root of 81972505 is about 9053.8668534500. The cubic root of 81972505 is about 434.3995856208.

The spelling of 81972505 in words is "eighty-one million, nine hundred seventy-two thousand, five hundred five".