81685999 has 2 divisors, whose sum is σ = 81686000. Its totient is φ = 81685998.

The previous prime is 81685963. The next prime is 81686009. The reversal of 81685999 is 99958618.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81685999 - 2¹⁷ = 81554927 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81685399) 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, 40842999 + 40843000.

It is an arithmetic number, because the mean of its divisors is an integer number (40843000).

Almost surely, 2^81685999 is an apocalyptic number.

81685999 is a deficient number, since it is larger than the sum of its proper divisors (1).

81685999 is an equidigital number, since it uses as much as digits as its factorization.

81685999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1399680, while the sum is 55.

The square root of 81685999 is about 9038.0307036434. The cubic root of 81685999 is about 433.8928979631.

The spelling of 81685999 in words is "eighty-one million, six hundred eighty-five thousand, nine hundred ninety-nine".