81799709 has 2 divisors, whose sum is σ = 81799710. Its totient is φ = 81799708.

The previous prime is 81799703. The next prime is 81799721. The reversal of 81799709 is 90799718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81396484 + 403225 = 9022^2 + 635^2 .

It is a cyclic number.

It is not a de Polignac number, because 81799709 - 2²⁰ = 80751133 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81799703) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40899854 + 40899855.

It is an arithmetic number, because the mean of its divisors is an integer number (40899855).

Almost surely, 2^81799709 is an apocalyptic number.

It is an amenable number.

81799709 is a deficient number, since it is larger than the sum of its proper divisors (1).

81799709 is an equidigital number, since it uses as much as digits as its factorization.

81799709 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 285768, while the sum is 50.

The square root of 81799709 is about 9044.3191562439. The cubic root of 81799709 is about 434.0941363894.

Subtracting 81799709 from its reverse (90799718), we obtain a palindrome (9000009).

The spelling of 81799709 in words is "eighty-one million, seven hundred ninety-nine thousand, seven hundred nine".