81179809 has 2 divisors, whose sum is σ = 81179810. Its totient is φ = 81179808.

The previous prime is 81179807. The next prime is 81179827. The reversal of 81179809 is 90897118.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73479184 + 7700625 = 8572^2 + 2775^2 .

It is a cyclic number.

It is not a de Polignac number, because 81179809 - 2¹ = 81179807 is a prime.

It is a super-2 number, since 2×81179809² = 13180322778552962, which contains 22 as substring.

Together with 81179807, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81179803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40589904 + 40589905.

It is an arithmetic number, because the mean of its divisors is an integer number (40589905).

Almost surely, 2^81179809 is an apocalyptic number.

It is an amenable number.

81179809 is a deficient number, since it is larger than the sum of its proper divisors (1).

81179809 is an equidigital number, since it uses as much as digits as its factorization.

81179809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36288, while the sum is 43.

The square root of 81179809 is about 9009.9838512619. The cubic root of 81179809 is about 432.9947942987.

The spelling of 81179809 in words is "eighty-one million, one hundred seventy-nine thousand, eight hundred nine".