81705191 has 2 divisors, whose sum is σ = 81705192.
Its totient is φ = 81705190.
The previous prime is 81705161. The next prime is 81705229. The reversal of 81705191 is 19150718.
It is a weak prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-81705191 is a prime.
It is a Sophie Germain prime.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (81705121) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (17) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40852595 + 40852596.
It is an arithmetic number, because the mean of its divisors is an integer number (40852596).
Almost surely, 281705191 is an apocalyptic number.
81705191 is a deficient number, since it is larger than the sum of its proper divisors (1).
81705191 is an equidigital number, since it uses as much as digits as its factorization.
81705191 is an odious number, because the sum of its binary digits is odd.
The product of its (nonzero) digits is 2520, while the sum is 32.
The square root of 81705191 is about 9039.0923770033.
The cubic root of 81705191 is about 433.9268761255.
The spelling of 81705191 in words is "eighty-one million, seven hundred five thousand, one hundred ninety-one".