81997823 has 2 divisors, whose sum is σ = 81997824. Its totient is φ = 81997822.

The previous prime is 81997789. The next prime is 81997831. The reversal of 81997823 is 32879918.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81997823 - 2⁸ = 81997567 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81997873) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40998911 + 40998912.

It is an arithmetic number, because the mean of its divisors is an integer number (40998912).

Almost surely, 2^81997823 is an apocalyptic number.

81997823 is a deficient number, since it is larger than the sum of its proper divisors (1).

81997823 is an equidigital number, since it uses as much as digits as its factorization.

81997823 is an odious number, because the sum of its binary digits is odd.

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

The square root of 81997823 is about 9055.2649326235. The cubic root of 81997823 is about 434.4443038533. Note that the first 3 decimals are identical.

The spelling of 81997823 in words is "eighty-one million, nine hundred ninety-seven thousand, eight hundred twenty-three".