81881993 has 4 divisors (see below), whose sum is σ = 84705540. Its totient is φ = 79058448.

The previous prime is 81881977. The next prime is 81882007. The reversal of 81881993 is 39918818.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 39918818 = 2 ⋅19959409.

It can be written as a sum of positive squares in 2 ways, for example, as 62283664 + 19598329 = 7892^2 + 4427^2 .

It is a cyclic number.

It is not a de Polignac number, because 81881993 - 2⁴ = 81881977 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81881903) 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, 1411730 + ... + 1411787.

It is an arithmetic number, because the mean of its divisors is an integer number (21176385).

Almost surely, 2^81881993 is an apocalyptic number.

It is an amenable number.

81881993 is a deficient number, since it is larger than the sum of its proper divisors (2823547).

81881993 is a wasteful number, since it uses less digits than its factorization.

81881993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2823546.

The product of its digits is 124416, while the sum is 47.

The square root of 81881993 is about 9048.8669456457. The cubic root of 81881993 is about 434.2396423340.

The spelling of 81881993 in words is "eighty-one million, eight hundred eighty-one thousand, nine hundred ninety-three".