81993947 has 4 divisors (see below), whose sum is σ = 93707376. Its totient is φ = 70280520.

The previous prime is 81993931. The next prime is 81993959. The reversal of 81993947 is 74939918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 74939918 = 2 ⋅37469959.

It is a cyclic number.

It is not a de Polignac number, because 81993947 - 2⁴ = 81993931 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81993895 and 81993904.

It is not an unprimeable number, because it can be changed into a prime (81993917) 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, 5856704 + ... + 5856717.

It is an arithmetic number, because the mean of its divisors is an integer number (23426844).

Almost surely, 2^81993947 is an apocalyptic number.

81993947 is a deficient number, since it is larger than the sum of its proper divisors (11713429).

81993947 is a wasteful number, since it uses less digits than its factorization.

81993947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11713428.

The product of its digits is 489888, while the sum is 50.

The square root of 81993947 is about 9055.0509109557. The cubic root of 81993947 is about 434.4374584169.

The spelling of 81993947 in words is "eighty-one million, nine hundred ninety-three thousand, nine hundred forty-seven".