81939973 has 4 divisors (see below), whose sum is σ = 81959788. Its totient is φ = 81920160.

The previous prime is 81939971. The next prime is 81940003. The reversal of 81939973 is 37993918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 37993918 = 2 ⋅18996959.

It can be written as a sum of positive squares in 2 ways, for example, as 77475204 + 4464769 = 8802^2 + 2113^2 .

It is a cyclic number.

It is not a de Polignac number, because 81939973 - 2¹ = 81939971 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81939971) 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, 1086 + ... + 12847.

It is an arithmetic number, because the mean of its divisors is an integer number (20489947).

Almost surely, 2^81939973 is an apocalyptic number.

It is an amenable number.

81939973 is a deficient number, since it is larger than the sum of its proper divisors (19815).

81939973 is a wasteful number, since it uses less digits than its factorization.

81939973 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19814.

The product of its digits is 367416, while the sum is 49.

The square root of 81939973 is about 9052.0700947352. The cubic root of 81939973 is about 434.3421120520.

The spelling of 81939973 in words is "eighty-one million, nine hundred thirty-nine thousand, nine hundred seventy-three".