81509809 has 2 divisors, whose sum is σ = 81509810. Its totient is φ = 81509808.

The previous prime is 81509801. The next prime is 81509833. The reversal of 81509809 is 90890518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 51840000 + 29669809 = 7200^2 + 5447^2 .

It is a cyclic number.

It is not a de Polignac number, because 81509809 - 2³ = 81509801 is a prime.

It is not a weakly prime, because it can be changed into another prime (81509801) 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, 40754904 + 40754905.

It is an arithmetic number, because the mean of its divisors is an integer number (40754905).

Almost surely, 2^81509809 is an apocalyptic number.

It is an amenable number.

81509809 is a deficient number, since it is larger than the sum of its proper divisors (1).

81509809 is an equidigital number, since it uses as much as digits as its factorization.

81509809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 25920, while the sum is 40.

The square root of 81509809 is about 9028.2782965524. The cubic root of 81509809 is about 433.5807162742.

The spelling of 81509809 in words is "eighty-one million, five hundred nine thousand, eight hundred nine".