81972839 has 4 divisors (see below), whose sum is σ = 88278456. Its totient is φ = 75667224.

The previous prime is 81972833. The next prime is 81972853. The reversal of 81972839 is 93827918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 93827918 = 2 ⋅46913959.

It is a cyclic number.

It is not a de Polignac number, because 81972839 - 2⁴ = 81972823 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81972793 and 81972802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81972833) 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, 3152789 + ... + 3152814.

It is an arithmetic number, because the mean of its divisors is an integer number (22069614).

Almost surely, 2^81972839 is an apocalyptic number.

81972839 is a deficient number, since it is larger than the sum of its proper divisors (6305617).

81972839 is a wasteful number, since it uses less digits than its factorization.

81972839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6305616.

The product of its digits is 217728, while the sum is 47.

The square root of 81972839 is about 9053.8852985887. The cubic root of 81972839 is about 434.4001756124.

The spelling of 81972839 in words is "eighty-one million, nine hundred seventy-two thousand, eight hundred thirty-nine".